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 $56.86   10.382%   $62.7632   $62.76   $62.75   $62.80  
  Purchase #2 $18.87   8.741%   $20.5194   $20.52   $20.50   $20.50  
  Purchase #3 $65.93   6.818%   $70.4251   $70.43   $70.45   $70.40  
  Purchase #4 $174.54   3.535%   $180.71   $180.71   $180.70   $180.70  
  Purchase #5 $92.42   12.261%   $103.7516   $103.75   $103.75   $103.80  
  Purchase #6 $101.84   13.546%   $115.6352   $115.64   $115.65   $115.60  
  Purchase #7 $59.91   8.814%   $65.1905   $65.19   $65.20   $65.20  
  7 purchase totals = $570.37       $618.9950   $619.00   $619.00   $619.00