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 $55.38   8.300%   $59.9765   $59.98   $60.00   $60.00  
  Purchase #2 $39.67   4.792%   $41.571   $41.57   $41.55   $41.60  
  Purchase #3 $5.77   7.703%   $6.2145   $6.21   $6.20   $6.20  
  Purchase #4 $86.93   9.472%   $95.164   $95.16   $95.15   $95.20  
  Purchase #5 $183.73   8.616%   $199.5602   $199.56   $199.55   $199.60  
  Purchase #6 $232.86   7.368%   $250.0171   $250.02   $250.00   $250.00  
  Purchase #7 $58.58   11.670%   $65.4163   $65.42   $65.40   $65.40  
  7 purchase totals = $662.92       $717.9196   $717.92   $717.85   $718.00