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 $61.86   3.381%   $63.9515   $63.95   $63.95   $64.00  
  Purchase #2 $144.77   9.663%   $158.7591   $158.76   $158.75   $158.80  
  Purchase #3 $226.55   4.833%   $237.4992   $237.50   $237.50   $237.50  
  Purchase #4 $227.38   7.334%   $244.056   $244.06   $244.05   $244.10  
  Purchase #5 $28.48   12.614%   $32.0725   $32.07   $32.05   $32.10  
  Purchase #6 $235.89   4.817%   $247.2528   $247.25   $247.25   $247.30  
  Purchase #7 $48.93   13.230%   $55.4034   $55.40   $55.40   $55.40  
  7 purchase totals = $973.86       $1,038.9945   $1,038.99   $1,038.95   $1,039.20