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 $59.35   9.510%   $64.9942   $64.99   $65.00   $65.00  
  Purchase #2 $181.75   7.407%   $195.2122   $195.21   $195.20   $195.20  
  Purchase #3 $176.39   12.226%   $197.9554   $197.96   $197.95   $198.00  
  Purchase #4 $109.29   6.165%   $116.0277   $116.03   $116.05   $116.00  
  Purchase #5 $115.59   4.727%   $121.0539   $121.05   $121.05   $121.10  
  Purchase #6 $246.86   13.295%   $279.68   $279.68   $279.70   $279.70  
  Purchase #7 $66.54   12.150%   $74.6246   $74.62   $74.60   $74.60  
  7 purchase totals = $955.77       $1,049.5480   $1,049.54   $1,049.55   $1,049.60