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 $125.33   7.371%   $134.5681   $134.57   $134.55   $134.60  
  Purchase #2 $187.33   4.394%   $195.5613   $195.56   $195.55   $195.60  
  Purchase #3 $97.76   6.735%   $104.3441   $104.34   $104.35   $104.30  
  Purchase #4 $55.85   7.421%   $59.9946   $59.99   $60.00   $60.00  
  Purchase #5 $69.42   7.652%   $74.732   $74.73   $74.75   $74.70  
  Purchase #6 $173.93   13.720%   $197.7932   $197.79   $197.80   $197.80  
  Purchase #7 $111.39   9.203%   $121.6412   $121.64   $121.65   $121.60  
  7 purchase totals = $821.01       $888.6345   $888.62   $888.65   $888.60