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 $38.96   13.569%   $44.2465   $44.25   $44.25   $44.20  
  Purchase #2 $154.96   12.155%   $173.7954   $173.80   $173.80   $173.80  
  Purchase #3 $213.69   5.612%   $225.6823   $225.68   $225.70   $225.70  
  Purchase #4 $165.29   12.115%   $185.3149   $185.31   $185.30   $185.30  
  Purchase #5 $195.73   3.411%   $202.4064   $202.41   $202.40   $202.40  
  Purchase #6 $129.71   6.120%   $137.6483   $137.65   $137.65   $137.60  
  Purchase #7 $85.77   8.130%   $92.7431   $92.74   $92.75   $92.70  
  7 purchase totals = $984.11       $1,061.8369   $1,061.84   $1,061.85   $1,061.70