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 $237.37   10.261%   $261.7265   $261.73   $261.75   $261.70  
  Purchase #2 $98.65   4.732%   $103.3181   $103.32   $103.30   $103.30  
  Purchase #3 $98.78   8.854%   $107.526   $107.53   $107.55   $107.50  
  Purchase #4 $58.88   11.109%   $65.421   $65.42   $65.40   $65.40  
  Purchase #5 $199.40   7.744%   $214.8415   $214.84   $214.85   $214.80  
  Purchase #6 $29.36   10.665%   $32.4912   $32.49   $32.50   $32.50  
  Purchase #7 $62.76   6.728%   $66.9825   $66.98   $67.00   $67.00  
  7 purchase totals = $785.20       $852.3068   $852.31   $852.35   $852.20