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 $241.27   9.271%   $263.6381   $263.64   $263.65   $263.60  
  Purchase #2 $203.54   3.609%   $210.8858   $210.89   $210.90   $210.90  
  Purchase #3 $24.62   13.432%   $27.927   $27.93   $27.95   $27.90  
  Purchase #4 $56.80   6.496%   $60.4897   $60.49   $60.50   $60.50  
  Purchase #5 $182.38   9.206%   $199.1699   $199.17   $199.15   $199.20  
  Purchase #6 $13.64   7.627%   $14.6803   $14.68   $14.70   $14.70  
  Purchase #7 $15.97   8.142%   $17.2703   $17.27   $17.25   $17.30  
  7 purchase totals = $738.22       $794.0611   $794.07   $794.10   $794.10