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 $87.63   10.319%   $96.6725   $96.67   $96.65   $96.70  
  Purchase #2 $185.86   6.482%   $197.9074   $197.91   $197.90   $197.90  
  Purchase #3 $117.31   12.693%   $132.2002   $132.20   $132.20   $132.20  
  Purchase #4 $66.60   8.617%   $72.3389   $72.34   $72.35   $72.30  
  Purchase #5 $250.85   3.190%   $258.8521   $258.85   $258.85   $258.90  
  Purchase #6 $45.45   6.110%   $48.227   $48.23   $48.25   $48.20  
  Purchase #7 $242.35   5.718%   $256.2076   $256.21   $256.20   $256.20  
  7 purchase totals = $996.05       $1,062.4057   $1,062.41   $1,062.40   $1,062.40