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 $132.93   11.299%   $147.9498   $147.95   $147.95   $147.90  
  Purchase #2 $143.69   5.474%   $151.5556   $151.56   $151.55   $151.60  
  Purchase #3 $244.88   4.414%   $255.689   $255.69   $255.70   $255.70  
  Purchase #4 $99.44   4.621%   $104.0351   $104.04   $104.05   $104.00  
  Purchase #5 $112.87   11.274%   $125.595   $125.60   $125.60   $125.60  
  Purchase #6 $116.39   5.645%   $122.9602   $122.96   $122.95   $123.00  
  Purchase #7 $72.57   9.821%   $79.6971   $79.70   $79.70   $79.70  
  7 purchase totals = $922.77       $987.4818   $987.50   $987.50   $987.50