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 $55.50   12.141%   $62.2383   $62.24   $62.25   $62.20  
  Purchase #2 $62.31   7.211%   $66.8032   $66.80   $66.80   $66.80  
  Purchase #3 $76.48   7.531%   $82.2397   $82.24   $82.25   $82.20  
  Purchase #4 $248.41   3.745%   $257.713   $257.71   $257.70   $257.70  
  Purchase #5 $153.32   4.253%   $159.8407   $159.84   $159.85   $159.80  
  Purchase #6 $245.45   8.278%   $265.7684   $265.77   $265.75   $265.80  
  Purchase #7 $53.88   8.610%   $58.5191   $58.52   $58.50   $58.50  
  7 purchase totals = $895.35       $953.1224   $953.12   $953.10   $953.00