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 $28.84   13.191%   $32.6443   $32.64   $32.65   $32.60  
  Purchase #2 $168.90   10.291%   $186.2815   $186.28   $186.30   $186.30  
  Purchase #3 $97.30   11.723%   $108.7065   $108.71   $108.70   $108.70  
  Purchase #4 $236.65   3.295%   $244.4476   $244.45   $244.45   $244.40  
  Purchase #5 $125.80   5.622%   $132.8725   $132.87   $132.85   $132.90  
  Purchase #6 $37.82   10.728%   $41.8773   $41.88   $41.90   $41.90  
  Purchase #7 $246.75   5.128%   $259.4033   $259.40   $259.40   $259.40  
  7 purchase totals = $942.06       $1,006.2330   $1,006.23   $1,006.25   $1,006.20