Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.30   11.653%   $252.6707   $252.67   $252.65   $252.70  
  Purchase #2 $131.51   4.340%   $137.2175   $137.22   $137.20   $137.20  
  Purchase #3 $149.53   4.859%   $156.7957   $156.80   $156.80   $156.80  
  Purchase #4 $208.79   12.335%   $234.5442   $234.54   $234.55   $234.50  
  Purchase #5 $174.89   3.806%   $181.5463   $181.55   $181.55   $181.50  
  Purchase #6 $135.91   11.815%   $151.9678   $151.97   $151.95   $152.00  
  Purchase #7 $115.96   10.139%   $127.7172   $127.72   $127.70   $127.70  
  7 purchase totals = $1,142.89       $1,242.4594   $1,242.47   $1,242.40   $1,242.40