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 $199.55   13.204%   $225.8986   $225.90   $225.90   $225.90  
  Purchase #2 $168.93   3.184%   $174.3087   $174.31   $174.30   $174.30  
  Purchase #3 $44.87   6.536%   $47.8027   $47.80   $47.80   $47.80  
  Purchase #4 $64.25   3.521%   $66.5122   $66.51   $66.50   $66.50  
  Purchase #5 $238.93   4.728%   $250.2266   $250.23   $250.25   $250.20  
  Purchase #6 $226.68   6.373%   $241.1263   $241.13   $241.15   $241.10  
  Purchase #7 $19.92   12.724%   $22.4546   $22.45   $22.45   $22.50  
  7 purchase totals = $963.13       $1,028.3297   $1,028.33   $1,028.35   $1,028.30