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 $239.83   12.183%   $269.0485   $269.05   $269.05   $269.00  
  Purchase #2 $81.90   8.429%   $88.8034   $88.80   $88.80   $88.80  
  Purchase #3 $231.86   13.267%   $262.6209   $262.62   $262.60   $262.60  
  Purchase #4 $85.38   11.221%   $94.9605   $94.96   $94.95   $95.00  
  Purchase #5 $71.76   4.707%   $75.1377   $75.14   $75.15   $75.10  
  Purchase #6 $250.41   6.147%   $265.8027   $265.80   $265.80   $265.80  
  Purchase #7 $108.29   5.169%   $113.8875   $113.89   $113.90   $113.90  
  7 purchase totals = $1,069.43       $1,170.2612   $1,170.26   $1,170.25   $1,170.20