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 $249.62   10.246%   $275.1961   $275.20   $275.20   $275.20  
  Purchase #2 $17.25   3.735%   $17.8943   $17.89   $17.90   $17.90  
  Purchase #3 $172.63   11.335%   $192.1976   $192.20   $192.20   $192.20  
  Purchase #4 $25.57   7.281%   $27.4318   $27.43   $27.45   $27.40  
  Purchase #5 $227.66   11.786%   $254.492   $254.49   $254.50   $254.50  
  Purchase #6 $83.72   10.670%   $92.6529   $92.65   $92.65   $92.70  
  Purchase #7 $85.36   6.781%   $91.1483   $91.15   $91.15   $91.10  
  7 purchase totals = $861.81       $951.0130   $951.01   $951.05   $951.00