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 $31.33   4.194%   $32.644   $32.64   $32.65   $32.60  
  Purchase #2 $250.34   3.532%   $259.182   $259.18   $259.20   $259.20  
  Purchase #3 $98.31   12.219%   $110.3225   $110.32   $110.30   $110.30  
  Purchase #4 $44.37   5.801%   $46.9439   $46.94   $46.95   $46.90  
  Purchase #5 $166.42   6.351%   $176.9893   $176.99   $177.00   $177.00  
  Purchase #6 $240.92   8.544%   $261.5042   $261.50   $261.50   $261.50  
  Purchase #7 $97.44   9.769%   $106.9589   $106.96   $106.95   $107.00  
  7 purchase totals = $929.13       $994.5448   $994.53   $994.55   $994.50