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 $41.41   3.697%   $42.9409   $42.94   $42.95   $42.90  
  Purchase #2 $81.41   4.435%   $85.0205   $85.02   $85.00   $85.00  
  Purchase #3 $172.52   9.388%   $188.7162   $188.72   $188.70   $188.70  
  Purchase #4 $44.79   13.687%   $50.9204   $50.92   $50.90   $50.90  
  Purchase #5 $148.62   12.575%   $167.309   $167.31   $167.30   $167.30  
  Purchase #6 $158.81   6.214%   $168.6785   $168.68   $168.70   $168.70  
  Purchase #7 $78.44   8.103%   $84.796   $84.80   $84.80   $84.80  
  7 purchase totals = $726.00       $788.3815   $788.39   $788.35   $788.30