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 $82.53   13.262%   $93.4751   $93.48   $93.50   $93.50  
  Purchase #2 $227.99   9.756%   $250.2327   $250.23   $250.25   $250.20  
  Purchase #3 $183.96   13.222%   $208.2832   $208.28   $208.30   $208.30  
  Purchase #4 $7.90   12.647%   $8.8991   $8.90   $8.90   $8.90  
  Purchase #5 $155.91   13.529%   $177.0031   $177.00   $177.00   $177.00  
  Purchase #6 $64.35   13.277%   $72.8937   $72.89   $72.90   $72.90  
  Purchase #7 $112.26   5.581%   $118.5252   $118.53   $118.55   $118.50  
  7 purchase totals = $834.90       $929.3121   $929.31   $929.40   $929.30