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 $216.91   11.221%   $241.2495   $241.25   $241.25   $241.20  
  Purchase #2 $159.77   3.125%   $164.7628   $164.76   $164.75   $164.80  
  Purchase #3 $64.93   3.670%   $67.3129   $67.31   $67.30   $67.30  
  Purchase #4 $38.51   7.676%   $41.466   $41.47   $41.45   $41.50  
  Purchase #5 $197.45   6.491%   $210.2665   $210.27   $210.25   $210.30  
  Purchase #6 $65.48   4.503%   $68.4286   $68.43   $68.45   $68.40  
  Purchase #7 $145.53   10.214%   $160.3944   $160.39   $160.40   $160.40  
  7 purchase totals = $888.58       $953.8807   $953.88   $953.85   $953.90