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 $87.66   3.342%   $90.5896   $90.59   $90.60   $90.60  
  Purchase #2 $176.92   9.281%   $193.3399   $193.34   $193.35   $193.30  
  Purchase #3 $95.92   3.124%   $98.9165   $98.92   $98.90   $98.90  
  Purchase #4 $172.58   7.349%   $185.2629   $185.26   $185.25   $185.30  
  Purchase #5 $166.27   13.103%   $188.0564   $188.06   $188.05   $188.10  
  Purchase #6 $220.37   11.173%   $244.9919   $244.99   $245.00   $245.00  
  Purchase #7 $144.94   10.120%   $159.6079   $159.61   $159.60   $159.60  
  7 purchase totals = $1,064.66       $1,160.7651   $1,160.77   $1,160.75   $1,160.80