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 $124.63   13.408%   $141.3404   $141.34   $141.35   $141.30  
  Purchase #2 $97.89   11.580%   $109.2257   $109.23   $109.25   $109.20  
  Purchase #3 $79.34   8.376%   $85.9855   $85.99   $86.00   $86.00  
  Purchase #4 $160.78   4.528%   $168.0601   $168.06   $168.05   $168.10  
  Purchase #5 $37.90   10.496%   $41.878   $41.88   $41.90   $41.90  
  Purchase #6 $176.63   9.863%   $194.051   $194.05   $194.05   $194.10  
  Purchase #7 $193.34   9.231%   $211.1872   $211.19   $211.20   $211.20  
  7 purchase totals = $870.51       $951.7279   $951.74   $951.80   $951.80