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 $208.63   8.816%   $227.0228   $227.02   $227.00   $227.00  
  Purchase #2 $207.38   5.371%   $218.5184   $218.52   $218.50   $218.50  
  Purchase #3 $127.57   13.569%   $144.88   $144.88   $144.90   $144.90  
  Purchase #4 $51.71   12.572%   $58.211   $58.21   $58.20   $58.20  
  Purchase #5 $21.92   11.123%   $24.3582   $24.36   $24.35   $24.40  
  Purchase #6 $121.35   10.703%   $134.3381   $134.34   $134.35   $134.30  
  Purchase #7 $53.32   3.565%   $55.2209   $55.22   $55.20   $55.20  
  7 purchase totals = $791.88       $862.5494   $862.55   $862.50   $862.50