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 $177.98   13.231%   $201.5285   $201.53   $201.55   $201.50  
  Purchase #2 $167.61   10.196%   $184.6995   $184.70   $184.70   $184.70  
  Purchase #3 $118.79   5.179%   $124.9421   $124.94   $124.95   $124.90  
  Purchase #4 $54.78   3.634%   $56.7707   $56.77   $56.75   $56.80  
  Purchase #5 $242.67   9.744%   $266.3158   $266.32   $266.30   $266.30  
  Purchase #6 $92.98   4.724%   $97.3724   $97.37   $97.35   $97.40  
  Purchase #7 $210.55   12.695%   $237.2793   $237.28   $237.30   $237.30  
  7 purchase totals = $1,065.36       $1,168.9083   $1,168.91   $1,168.90   $1,168.90