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 $73.26   3.549%   $75.86   $75.86   $75.85   $75.90  
  Purchase #2 $59.90   5.798%   $63.373   $63.37   $63.35   $63.40  
  Purchase #3 $183.45   10.603%   $202.9012   $202.90   $202.90   $202.90  
  Purchase #4 $32.49   3.519%   $33.6333   $33.63   $33.65   $33.60  
  Purchase #5 $115.72   6.544%   $123.2927   $123.29   $123.30   $123.30  
  Purchase #6 $131.63   3.638%   $136.4187   $136.42   $136.40   $136.40  
  Purchase #7 $154.77   9.141%   $168.9175   $168.92   $168.90   $168.90  
  7 purchase totals = $751.22       $804.3964   $804.39   $804.35   $804.40