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 $191.98   9.148%   $209.5423   $209.54   $209.55   $209.50  
  Purchase #2 $160.37   10.295%   $176.8801   $176.88   $176.90   $176.90  
  Purchase #3 $187.67   8.281%   $203.211   $203.21   $203.20   $203.20  
  Purchase #4 $39.77   4.374%   $41.5095   $41.51   $41.50   $41.50  
  Purchase #5 $46.59   7.436%   $50.0544   $50.05   $50.05   $50.10  
  Purchase #6 $114.88   9.240%   $125.4949   $125.49   $125.50   $125.50  
  Purchase #7 $53.73   8.868%   $58.4948   $58.49   $58.50   $58.50  
  7 purchase totals = $794.99       $865.1870   $865.17   $865.20   $865.20