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 $56.33   13.638%   $64.0123   $64.01   $64.00   $64.00  
  Purchase #2 $95.43   9.559%   $104.5522   $104.55   $104.55   $104.60  
  Purchase #3 $136.75   12.418%   $153.7316   $153.73   $153.75   $153.70  
  Purchase #4 $34.50   5.256%   $36.3133   $36.31   $36.30   $36.30  
  Purchase #5 $31.45   9.674%   $34.4925   $34.49   $34.50   $34.50  
  Purchase #6 $109.82   5.280%   $115.6185   $115.62   $115.60   $115.60  
  Purchase #7 $163.70   11.338%   $182.2603   $182.26   $182.25   $182.30  
  7 purchase totals = $627.98       $690.9807   $690.97   $690.95   $691.00