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 $93.91   3.656%   $97.3433   $97.34   $97.35   $97.30  
  Purchase #2 $179.69   8.172%   $194.3743   $194.37   $194.35   $194.40  
  Purchase #3 $158.68   7.790%   $171.0412   $171.04   $171.05   $171.00  
  Purchase #4 $157.68   9.248%   $172.2622   $172.26   $172.25   $172.30  
  Purchase #5 $127.99   4.491%   $133.738   $133.74   $133.75   $133.70  
  Purchase #6 $202.30   11.129%   $224.814   $224.81   $224.80   $224.80  
  Purchase #7 $147.56   9.302%   $161.286   $161.29   $161.30   $161.30  
  7 purchase totals = $1,067.81       $1,154.8590   $1,154.85   $1,154.85   $1,154.80