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 $236.53   6.641%   $252.238   $252.24   $252.25   $252.20  
  Purchase #2 $213.51   10.844%   $236.663   $236.66   $236.65   $236.70  
  Purchase #3 $112.38   10.610%   $124.3035   $124.30   $124.30   $124.30  
  Purchase #4 $121.61   12.754%   $137.1201   $137.12   $137.10   $137.10  
  Purchase #5 $119.59   5.440%   $126.0957   $126.10   $126.10   $126.10  
  Purchase #6 $14.79   12.111%   $16.5812   $16.58   $16.60   $16.60  
  Purchase #7 $42.81   13.546%   $48.609   $48.61   $48.60   $48.60  
  7 purchase totals = $861.22       $941.6105   $941.61   $941.60   $941.60