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 $147.98   3.726%   $153.4937   $153.49   $153.50   $153.50  
  Purchase #2 $248.50   3.339%   $256.7974   $256.80   $256.80   $256.80  
  Purchase #3 $105.25   10.745%   $116.5591   $116.56   $116.55   $116.60  
  Purchase #4 $39.75   12.447%   $44.6977   $44.70   $44.70   $44.70  
  Purchase #5 $149.36   5.198%   $157.1237   $157.12   $157.10   $157.10  
  Purchase #6 $119.46   8.271%   $129.3405   $129.34   $129.35   $129.30  
  Purchase #7 $43.34   9.161%   $47.3104   $47.31   $47.30   $47.30  
  7 purchase totals = $853.64       $905.3225   $905.32   $905.30   $905.30