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 $88.67   6.751%   $94.6561   $94.66   $94.65   $94.70  
  Purchase #2 $111.86   9.547%   $122.5393   $122.54   $122.55   $122.50  
  Purchase #3 $239.68   4.581%   $250.6597   $250.66   $250.65   $250.70  
  Purchase #4 $14.63   3.720%   $15.1742   $15.17   $15.15   $15.20  
  Purchase #5 $182.47   8.190%   $197.4143   $197.41   $197.40   $197.40  
  Purchase #6 $144.91   5.309%   $152.6033   $152.60   $152.60   $152.60  
  Purchase #7 $125.80   13.313%   $142.5478   $142.55   $142.55   $142.50  
  7 purchase totals = $908.02       $975.5947   $975.59   $975.55   $975.60