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 $24.61   8.398%   $26.6767   $26.68   $26.70   $26.70  
  Purchase #2 $168.29   7.236%   $180.4675   $180.47   $180.45   $180.50  
  Purchase #3 $12.98   11.506%   $14.4735   $14.47   $14.45   $14.50  
  Purchase #4 $194.33   6.657%   $207.2665   $207.27   $207.25   $207.30  
  Purchase #5 $83.34   9.759%   $91.4732   $91.47   $91.45   $91.50  
  Purchase #6 $248.84   7.581%   $267.7046   $267.70   $267.70   $267.70  
  Purchase #7 $42.93   9.596%   $47.0496   $47.05   $47.05   $47.00  
  7 purchase totals = $775.32       $835.1116   $835.11   $835.05   $835.20