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 $40.81   6.836%   $43.5998   $43.60   $43.60   $43.60  
  Purchase #2 $131.84   3.708%   $136.7286   $136.73   $136.75   $136.70  
  Purchase #3 $215.62   9.596%   $236.3109   $236.31   $236.30   $236.30  
  Purchase #4 $60.43   9.460%   $66.1467   $66.15   $66.15   $66.10  
  Purchase #5 $167.64   10.322%   $184.9438   $184.94   $184.95   $184.90  
  Purchase #6 $166.36   12.195%   $186.6476   $186.65   $186.65   $186.60  
  Purchase #7 $75.65   7.316%   $81.1846   $81.18   $81.20   $81.20  
  7 purchase totals = $858.35       $935.5620   $935.56   $935.60   $935.40