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 $73.77   13.768%   $83.9267   $83.93   $83.95   $83.90  
  Purchase #2 $239.29   5.236%   $251.8192   $251.82   $251.80   $251.80  
  Purchase #3 $42.28   5.695%   $44.6878   $44.69   $44.70   $44.70  
  Purchase #4 $147.87   11.117%   $164.3087   $164.31   $164.30   $164.30  
  Purchase #5 $184.70   5.103%   $194.1252   $194.13   $194.15   $194.10  
  Purchase #6 $178.74   3.155%   $184.3792   $184.38   $184.40   $184.40  
  Purchase #7 $9.95   5.475%   $10.4948   $10.49   $10.50   $10.50  
  7 purchase totals = $876.60       $933.7416   $933.75   $933.80   $933.70