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 $87.86   6.426%   $93.5059   $93.51   $93.50   $93.50  
  Purchase #2 $22.59   4.445%   $23.5941   $23.59   $23.60   $23.60  
  Purchase #3 $159.41   12.254%   $178.9441   $178.94   $178.95   $178.90  
  Purchase #4 $196.42   10.453%   $216.9518   $216.95   $216.95   $217.00  
  Purchase #5 $69.54   9.366%   $76.0531   $76.05   $76.05   $76.10  
  Purchase #6 $120.55   13.282%   $136.5615   $136.56   $136.55   $136.60  
  Purchase #7 $139.34   9.794%   $152.987   $152.99   $153.00   $153.00  
  7 purchase totals = $795.71       $878.5975   $878.59   $878.60   $878.70