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 $114.71   4.141%   $119.4601   $119.46   $119.45   $119.50  
  Purchase #2 $195.92   10.603%   $216.6934   $216.69   $216.70   $216.70  
  Purchase #3 $163.81   7.703%   $176.4283   $176.43   $176.45   $176.40  
  Purchase #4 $143.25   5.231%   $150.7434   $150.74   $150.75   $150.70  
  Purchase #5 $115.70   12.442%   $130.0954   $130.10   $130.10   $130.10  
  Purchase #6 $140.42   6.172%   $149.0867   $149.09   $149.10   $149.10  
  Purchase #7 $58.54   9.651%   $64.1897   $64.19   $64.20   $64.20  
  7 purchase totals = $932.35       $1,006.6970   $1,006.70   $1,006.75   $1,006.70