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 $153.94   10.307%   $169.8066   $169.81   $169.80   $169.80  
  Purchase #2 $233.38   6.261%   $247.9919   $247.99   $248.00   $248.00  
  Purchase #3 $133.29   4.319%   $139.0468   $139.05   $139.05   $139.00  
  Purchase #4 $86.64   10.578%   $95.8048   $95.80   $95.80   $95.80  
  Purchase #5 $158.26   12.846%   $178.5901   $178.59   $178.60   $178.60  
  Purchase #6 $168.55   9.249%   $184.1392   $184.14   $184.15   $184.10  
  Purchase #7 $169.64   4.131%   $176.6478   $176.65   $176.65   $176.60  
  7 purchase totals = $1,103.70       $1,192.0272   $1,192.03   $1,192.05   $1,191.90