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 $244.32   8.618%   $265.3755   $265.38   $265.40   $265.40  
  Purchase #2 $76.46   6.389%   $81.345   $81.35   $81.35   $81.30  
  Purchase #3 $81.29   10.261%   $89.6312   $89.63   $89.65   $89.60  
  Purchase #4 $121.76   3.712%   $126.2797   $126.28   $126.30   $126.30  
  Purchase #5 $11.36   5.430%   $11.9768   $11.98   $12.00   $12.00  
  Purchase #6 $215.95   7.427%   $231.9886   $231.99   $232.00   $232.00  
  Purchase #7 $54.74   12.837%   $61.767   $61.77   $61.75   $61.80  
  7 purchase totals = $805.88       $868.3638   $868.38   $868.45   $868.40