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 $182.52   6.546%   $194.4678   $194.47   $194.45   $194.50  
  Purchase #2 $68.41   6.765%   $73.0379   $73.04   $73.05   $73.00  
  Purchase #3 $116.72   13.282%   $132.2228   $132.22   $132.20   $132.20  
  Purchase #4 $224.69   8.134%   $242.9663   $242.97   $242.95   $243.00  
  Purchase #5 $96.40   8.834%   $104.916   $104.92   $104.90   $104.90  
  Purchase #6 $245.72   6.295%   $261.1881   $261.19   $261.20   $261.20  
  Purchase #7 $38.70   4.567%   $40.4674   $40.47   $40.45   $40.50  
  7 purchase totals = $973.16       $1,049.2663   $1,049.28   $1,049.20   $1,049.30