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 $72.68   8.173%   $78.6201   $78.62   $78.60   $78.60  
  Purchase #2 $179.41   13.347%   $203.3559   $203.36   $203.35   $203.40  
  Purchase #3 $249.93   9.298%   $273.1685   $273.17   $273.15   $273.20  
  Purchase #4 $48.61   10.733%   $53.8273   $53.83   $53.85   $53.80  
  Purchase #5 $67.98   8.672%   $73.8752   $73.88   $73.90   $73.90  
  Purchase #6 $166.69   12.708%   $187.873   $187.87   $187.85   $187.90  
  Purchase #7 $39.91   13.359%   $45.2416   $45.24   $45.25   $45.20  
  7 purchase totals = $825.21       $915.9616   $915.97   $915.95   $916.00