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 $29.76   9.647%   $32.6309   $32.63   $32.65   $32.60  
  Purchase #2 $199.93   4.861%   $209.6486   $209.65   $209.65   $209.60  
  Purchase #3 $31.75   6.184%   $33.7134   $33.71   $33.70   $33.70  
  Purchase #4 $180.37   8.662%   $195.9936   $195.99   $196.00   $196.00  
  Purchase #5 $235.99   12.295%   $265.005   $265.01   $265.00   $265.00  
  Purchase #6 $169.47   13.435%   $192.2383   $192.24   $192.25   $192.20  
  Purchase #7 $22.39   3.227%   $23.1125   $23.11   $23.10   $23.10  
  7 purchase totals = $869.66       $952.3423   $952.34   $952.35   $952.20