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 $58.39   4.489%   $61.0111   $61.01   $61.00   $61.00  
  Purchase #2 $243.59   7.452%   $261.7423   $261.74   $261.75   $261.70  
  Purchase #3 $26.38   5.792%   $27.9079   $27.91   $27.90   $27.90  
  Purchase #4 $123.88   12.517%   $139.3861   $139.39   $139.40   $139.40  
  Purchase #5 $7.89   5.737%   $8.3426   $8.34   $8.35   $8.30  
  Purchase #6 $85.57   6.486%   $91.1201   $91.12   $91.10   $91.10  
  Purchase #7 $128.81   4.668%   $134.8229   $134.82   $134.80   $134.80  
  7 purchase totals = $674.51       $724.3330   $724.33   $724.30   $724.20