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 $134.76   8.523%   $146.2456   $146.25   $146.25   $146.20  
  Purchase #2 $234.39   10.498%   $258.9963   $259.00   $259.00   $259.00  
  Purchase #3 $95.88   6.368%   $101.9856   $101.99   $102.00   $102.00  
  Purchase #4 $93.27   4.732%   $97.6835   $97.68   $97.70   $97.70  
  Purchase #5 $28.39   12.747%   $32.0089   $32.01   $32.00   $32.00  
  Purchase #6 $195.78   12.817%   $220.8731   $220.87   $220.85   $220.90  
  Purchase #7 $103.80   13.186%   $117.4871   $117.49   $117.50   $117.50  
  7 purchase totals = $886.27       $975.2801   $975.29   $975.30   $975.30