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 $60.59   4.766%   $63.4777   $63.48   $63.50   $63.50  
  Purchase #2 $68.99   13.800%   $78.5106   $78.51   $78.50   $78.50  
  Purchase #3 $10.73   9.699%   $11.7707   $11.77   $11.75   $11.80  
  Purchase #4 $73.75   13.763%   $83.9002   $83.90   $83.90   $83.90  
  Purchase #5 $223.42   5.712%   $236.1818   $236.18   $236.20   $236.20  
  Purchase #6 $203.50   4.651%   $212.9648   $212.96   $212.95   $213.00  
  Purchase #7 $76.88   12.556%   $86.5331   $86.53   $86.55   $86.50  
  7 purchase totals = $717.86       $773.3389   $773.33   $773.35   $773.40