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 $242.29   6.188%   $257.2829   $257.28   $257.30   $257.30  
  Purchase #2 $33.63   4.398%   $35.109   $35.11   $35.10   $35.10  
  Purchase #3 $203.86   7.238%   $218.6154   $218.62   $218.60   $218.60  
  Purchase #4 $214.47   4.736%   $224.6273   $224.63   $224.65   $224.60  
  Purchase #5 $160.99   5.578%   $169.97   $169.97   $169.95   $170.00  
  Purchase #6 $176.56   10.556%   $195.1977   $195.20   $195.20   $195.20  
  Purchase #7 $29.85   8.153%   $32.2837   $32.28   $32.30   $32.30  
  7 purchase totals = $1,061.65       $1,133.0860   $1,133.09   $1,133.10   $1,133.10