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 $217.93   11.711%   $243.4518   $243.45   $243.45   $243.50  
  Purchase #2 $232.71   7.124%   $249.2883   $249.29   $249.30   $249.30  
  Purchase #3 $156.71   11.129%   $174.1503   $174.15   $174.15   $174.20  
  Purchase #4 $6.83   6.554%   $7.2776   $7.28   $7.30   $7.30  
  Purchase #5 $225.69   9.516%   $247.1667   $247.17   $247.15   $247.20  
  Purchase #6 $140.61   8.642%   $152.7615   $152.76   $152.75   $152.80  
  Purchase #7 $160.91   11.405%   $179.2618   $179.26   $179.25   $179.30  
  7 purchase totals = $1,141.39       $1,253.3580   $1,253.36   $1,253.35   $1,253.60