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 $58.33   9.423%   $63.8264   $63.83   $63.85   $63.80  
  Purchase #2 $231.42   10.228%   $255.0896   $255.09   $255.10   $255.10  
  Purchase #3 $241.38   9.687%   $264.7625   $264.76   $264.75   $264.80  
  Purchase #4 $13.37   10.588%   $14.7856   $14.79   $14.80   $14.80  
  Purchase #5 $45.83   11.344%   $51.029   $51.03   $51.05   $51.00  
  Purchase #6 $124.82   4.679%   $130.6603   $130.66   $130.65   $130.70  
  Purchase #7 $245.36   5.169%   $258.0427   $258.04   $258.05   $258.00  
  7 purchase totals = $960.51       $1,038.1961   $1,038.20   $1,038.25   $1,038.20