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 $245.53   5.714%   $259.5596   $259.56   $259.55   $259.60  
  Purchase #2 $89.32   5.193%   $93.9584   $93.96   $93.95   $94.00  
  Purchase #3 $45.90   6.638%   $48.9468   $48.95   $48.95   $48.90  
  Purchase #4 $137.86   11.686%   $153.9703   $153.97   $153.95   $154.00  
  Purchase #5 $62.84   9.322%   $68.6979   $68.70   $68.70   $68.70  
  Purchase #6 $208.69   9.179%   $227.8457   $227.85   $227.85   $227.80  
  Purchase #7 $163.92   4.636%   $171.5193   $171.52   $171.50   $171.50  
  7 purchase totals = $954.06       $1,024.4980   $1,024.51   $1,024.45   $1,024.50