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 $107.76   9.507%   $118.0047   $118.00   $118.00   $118.00  
  Purchase #2 $159.43   10.223%   $175.7285   $175.73   $175.75   $175.70  
  Purchase #3 $56.83   11.161%   $63.1728   $63.17   $63.15   $63.20  
  Purchase #4 $90.33   8.276%   $97.8057   $97.81   $97.80   $97.80  
  Purchase #5 $91.78   5.796%   $97.0996   $97.10   $97.10   $97.10  
  Purchase #6 $246.46   3.223%   $254.4034   $254.40   $254.40   $254.40  
  Purchase #7 $201.66   4.429%   $210.5915   $210.59   $210.60   $210.60  
  7 purchase totals = $954.25       $1,016.8062   $1,016.80   $1,016.80   $1,016.80