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 $195.89   11.167%   $217.765   $217.77   $217.75   $217.80  
  Purchase #2 $88.96   7.716%   $95.8242   $95.82   $95.80   $95.80  
  Purchase #3 $106.81   4.311%   $111.4146   $111.41   $111.40   $111.40  
  Purchase #4 $148.95   6.420%   $158.5126   $158.51   $158.50   $158.50  
  Purchase #5 $162.48   9.161%   $177.3648   $177.36   $177.35   $177.40  
  Purchase #6 $52.69   11.529%   $58.7646   $58.76   $58.75   $58.80  
  Purchase #7 $6.51   8.243%   $7.0466   $7.05   $7.05   $7.00  
  7 purchase totals = $762.29       $826.6924   $826.68   $826.60   $826.70