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 $223.42   10.305%   $246.4434   $246.44   $246.45   $246.40  
  Purchase #2 $108.29   3.601%   $112.1895   $112.19   $112.20   $112.20  
  Purchase #3 $108.67   11.715%   $121.4007   $121.40   $121.40   $121.40  
  Purchase #4 $97.89   6.146%   $103.9063   $103.91   $103.90   $103.90  
  Purchase #5 $219.48   6.157%   $232.9934   $232.99   $233.00   $233.00  
  Purchase #6 $48.37   9.420%   $52.9265   $52.93   $52.95   $52.90  
  Purchase #7 $119.59   6.121%   $126.9101   $126.91   $126.90   $126.90  
  7 purchase totals = $925.71       $996.7699   $996.77   $996.80   $996.70