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 $118.98   10.223%   $131.1433   $131.14   $131.15   $131.10  
  Purchase #2 $99.46   7.750%   $107.1682   $107.17   $107.15   $107.20  
  Purchase #3 $148.44   13.439%   $168.3889   $168.39   $168.40   $168.40  
  Purchase #4 $203.68   9.711%   $223.4594   $223.46   $223.45   $223.50  
  Purchase #5 $244.52   9.725%   $268.2996   $268.30   $268.30   $268.30  
  Purchase #6 $206.93   9.380%   $226.34   $226.34   $226.35   $226.30  
  Purchase #7 $239.54   5.194%   $251.9817   $251.98   $252.00   $252.00  
  7 purchase totals = $1,261.55       $1,376.7811   $1,376.78   $1,376.80   $1,376.80