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 $59.37   4.301%   $61.9235   $61.92   $61.90   $61.90  
  Purchase #2 $88.96   7.401%   $95.5439   $95.54   $95.55   $95.50  
  Purchase #3 $85.35   9.211%   $93.2116   $93.21   $93.20   $93.20  
  Purchase #4 $146.27   7.824%   $157.7142   $157.71   $157.70   $157.70  
  Purchase #5 $206.71   13.790%   $235.2153   $235.22   $235.20   $235.20  
  Purchase #6 $69.42   7.354%   $74.5251   $74.53   $74.55   $74.50  
  Purchase #7 $20.95   7.125%   $22.4427   $22.44   $22.45   $22.40  
  7 purchase totals = $677.03       $740.5763   $740.57   $740.55   $740.40