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 $40.82   13.632%   $46.3846   $46.38   $46.40   $46.40  
  Purchase #2 $217.91   12.278%   $244.665   $244.67   $244.65   $244.70  
  Purchase #3 $160.57   12.576%   $180.7633   $180.76   $180.75   $180.80  
  Purchase #4 $214.65   5.558%   $226.5802   $226.58   $226.60   $226.60  
  Purchase #5 $202.40   13.292%   $229.303   $229.30   $229.30   $229.30  
  Purchase #6 $96.69   4.728%   $101.2615   $101.26   $101.25   $101.30  
  Purchase #7 $85.70   13.648%   $97.3963   $97.40   $97.40   $97.40  
  7 purchase totals = $1,018.74       $1,126.3539   $1,126.35   $1,126.35   $1,126.50