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 $168.61   10.248%   $185.8892   $185.89   $185.90   $185.90  
  Purchase #2 $162.67   6.468%   $173.1915   $173.19   $173.20   $173.20  
  Purchase #3 $248.51   6.477%   $264.606   $264.61   $264.60   $264.60  
  Purchase #4 $155.82   7.311%   $167.212   $167.21   $167.20   $167.20  
  Purchase #5 $223.76   9.355%   $244.6927   $244.69   $244.70   $244.70  
  Purchase #6 $30.88   11.742%   $34.5059   $34.51   $34.50   $34.50  
  Purchase #7 $220.93   13.803%   $251.425   $251.43   $251.45   $251.40  
  7 purchase totals = $1,211.18       $1,321.5223   $1,321.53   $1,321.55   $1,321.50