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 $226.94   8.854%   $247.0333   $247.03   $247.05   $247.00  
  Purchase #2 $157.46   9.201%   $171.9479   $171.95   $171.95   $171.90  
  Purchase #3 $183.92   8.551%   $199.647   $199.65   $199.65   $199.60  
  Purchase #4 $236.68   4.737%   $247.8915   $247.89   $247.90   $247.90  
  Purchase #5 $47.81   10.464%   $52.8128   $52.81   $52.80   $52.80  
  Purchase #6 $233.71   7.749%   $251.8202   $251.82   $251.80   $251.80  
  Purchase #7 $29.93   13.454%   $33.9568   $33.96   $33.95   $34.00  
  7 purchase totals = $1,116.45       $1,205.1095   $1,205.11   $1,205.10   $1,205.00