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 $60.79   3.682%   $63.0283   $63.03   $63.05   $63.00  
  Purchase #2 $26.89   10.658%   $29.7559   $29.76   $29.75   $29.80  
  Purchase #3 $87.27   9.676%   $95.7142   $95.71   $95.70   $95.70  
  Purchase #4 $242.34   13.732%   $275.6181   $275.62   $275.60   $275.60  
  Purchase #5 $28.82   12.199%   $32.3358   $32.34   $32.35   $32.30  
  Purchase #6 $32.99   13.461%   $37.4308   $37.43   $37.45   $37.40  
  Purchase #7 $17.38   9.640%   $19.0554   $19.06   $19.05   $19.10  
  7 purchase totals = $496.48       $552.9385   $552.95   $552.95   $552.90