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 $220.95   11.595%   $246.5692   $246.57   $246.55   $246.60  
  Purchase #2 $117.83   9.357%   $128.8554   $128.86   $128.85   $128.90  
  Purchase #3 $21.27   12.769%   $23.986   $23.99   $24.00   $24.00  
  Purchase #4 $125.62   12.388%   $141.1818   $141.18   $141.20   $141.20  
  Purchase #5 $67.97   6.557%   $72.4268   $72.43   $72.45   $72.40  
  Purchase #6 $69.40   3.549%   $71.863   $71.86   $71.85   $71.90  
  Purchase #7 $68.58   10.271%   $75.6239   $75.62   $75.60   $75.60  
  7 purchase totals = $691.62       $760.5061   $760.51   $760.50   $760.60