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 $88.57   6.541%   $94.3634   $94.36   $94.35   $94.40  
  Purchase #2 $210.35   5.447%   $221.8078   $221.81   $221.80   $221.80  
  Purchase #3 $137.80   10.299%   $151.992   $151.99   $152.00   $152.00  
  Purchase #4 $17.51   11.843%   $19.5837   $19.58   $19.60   $19.60  
  Purchase #5 $228.42   12.664%   $257.3471   $257.35   $257.35   $257.30  
  Purchase #6 $46.64   11.566%   $52.0344   $52.03   $52.05   $52.00  
  Purchase #7 $10.79   10.445%   $11.917   $11.92   $11.90   $11.90  
  7 purchase totals = $740.08       $809.0454   $809.04   $809.05   $809.00