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 $87.39   6.705%   $93.2495   $93.25   $93.25   $93.20  
  Purchase #2 $247.96   5.304%   $261.1118   $261.11   $261.10   $261.10  
  Purchase #3 $88.31   11.697%   $98.6396   $98.64   $98.65   $98.60  
  Purchase #4 $32.85   6.835%   $35.0953   $35.10   $35.10   $35.10  
  Purchase #5 $107.75   7.611%   $115.9509   $115.95   $115.95   $116.00  
  Purchase #6 $183.78   8.632%   $199.6439   $199.64   $199.65   $199.60  
  Purchase #7 $28.77   8.577%   $31.2376   $31.24   $31.25   $31.20  
  7 purchase totals = $776.81       $834.9286   $834.93   $834.95   $834.80