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 $52.73   12.752%   $59.4541   $59.45   $59.45   $59.50  
  Purchase #2 $137.67   8.422%   $149.2646   $149.26   $149.25   $149.30  
  Purchase #3 $129.99   10.185%   $143.2295   $143.23   $143.25   $143.20  
  Purchase #4 $184.61   13.503%   $209.5379   $209.54   $209.55   $209.50  
  Purchase #5 $215.30   5.732%   $227.641   $227.64   $227.65   $227.60  
  Purchase #6 $12.32   6.487%   $13.1192   $13.12   $13.10   $13.10  
  Purchase #7 $94.44   7.817%   $101.8224   $101.82   $101.80   $101.80  
  7 purchase totals = $827.06       $904.0687   $904.06   $904.05   $904.00