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 $60.93   6.663%   $64.9898   $64.99   $65.00   $65.00  
  Purchase #2 $217.53   6.675%   $232.0501   $232.05   $232.05   $232.10  
  Purchase #3 $9.70   8.794%   $10.553   $10.55   $10.55   $10.60  
  Purchase #4 $84.92   4.740%   $88.9452   $88.95   $88.95   $88.90  
  Purchase #5 $244.44   7.430%   $262.6019   $262.60   $262.60   $262.60  
  Purchase #6 $64.31   12.186%   $72.1468   $72.15   $72.15   $72.10  
  Purchase #7 $26.45   11.126%   $29.3928   $29.39   $29.40   $29.40  
  7 purchase totals = $708.28       $760.6796   $760.68   $760.70   $760.70