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 $242.91   8.336%   $263.159   $263.16   $263.15   $263.20  
  Purchase #2 $29.65   6.759%   $31.654   $31.65   $31.65   $31.70  
  Purchase #3 $131.96   4.114%   $137.3888   $137.39   $137.40   $137.40  
  Purchase #4 $179.38   9.789%   $196.9395   $196.94   $196.95   $196.90  
  Purchase #5 $101.67   10.820%   $112.6707   $112.67   $112.65   $112.70  
  Purchase #6 $107.74   10.103%   $118.625   $118.63   $118.65   $118.60  
  Purchase #7 $13.25   7.648%   $14.2634   $14.26   $14.25   $14.30  
  7 purchase totals = $806.56       $874.7004   $874.70   $874.70   $874.80