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 $6.25   11.123%   $6.9452   $6.95   $6.95   $6.90  
  Purchase #2 $144.84   7.271%   $155.3713   $155.37   $155.35   $155.40  
  Purchase #3 $70.80   7.399%   $76.0385   $76.04   $76.05   $76.00  
  Purchase #4 $238.29   8.523%   $258.5995   $258.60   $258.60   $258.60  
  Purchase #5 $68.79   7.208%   $73.7484   $73.75   $73.75   $73.70  
  Purchase #6 $195.29   3.338%   $201.8088   $201.81   $201.80   $201.80  
  Purchase #7 $231.90   11.373%   $258.274   $258.27   $258.25   $258.30  
  7 purchase totals = $956.16       $1,030.7857   $1,030.79   $1,030.75   $1,030.70