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 $239.38   11.532%   $266.9853   $266.99   $267.00   $267.00  
  Purchase #2 $116.27   12.647%   $130.9747   $130.97   $130.95   $131.00  
  Purchase #3 $114.84   12.645%   $129.3615   $129.36   $129.35   $129.40  
  Purchase #4 $207.32   5.846%   $219.4399   $219.44   $219.45   $219.40  
  Purchase #5 $185.41   5.541%   $195.6836   $195.68   $195.70   $195.70  
  Purchase #6 $232.82   5.726%   $246.1513   $246.15   $246.15   $246.20  
  Purchase #7 $138.72   4.136%   $144.4575   $144.46   $144.45   $144.50  
  7 purchase totals = $1,234.76       $1,333.0538   $1,333.05   $1,333.05   $1,333.20