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 $221.71   11.687%   $247.6212   $247.62   $247.60   $247.60  
  Purchase #2 $119.53   13.824%   $136.0538   $136.05   $136.05   $136.10  
  Purchase #3 $203.99   6.432%   $217.1106   $217.11   $217.10   $217.10  
  Purchase #4 $21.98   9.480%   $24.0637   $24.06   $24.05   $24.10  
  Purchase #5 $234.75   3.634%   $243.2808   $243.28   $243.30   $243.30  
  Purchase #6 $64.42   7.545%   $69.2805   $69.28   $69.30   $69.30  
  Purchase #7 $244.61   8.586%   $265.6122   $265.61   $265.60   $265.60  
  7 purchase totals = $1,110.99       $1,203.0228   $1,203.01   $1,203.00   $1,203.10