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 $183.94   6.410%   $195.7306   $195.73   $195.75   $195.70  
  Purchase #2 $77.39   8.637%   $84.0742   $84.07   $84.05   $84.10  
  Purchase #3 $224.83   9.201%   $245.5166   $245.52   $245.50   $245.50  
  Purchase #4 $32.82   8.570%   $35.6327   $35.63   $35.65   $35.60  
  Purchase #5 $90.33   3.187%   $93.2088   $93.21   $93.20   $93.20  
  Purchase #6 $237.71   5.635%   $251.105   $251.11   $251.10   $251.10  
  Purchase #7 $51.33   7.704%   $55.2845   $55.28   $55.30   $55.30  
  7 purchase totals = $898.35       $960.5524   $960.55   $960.55   $960.50