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 $64.61   13.441%   $73.2942   $73.29   $73.30   $73.30  
  Purchase #2 $109.96   8.508%   $119.3154   $119.32   $119.30   $119.30  
  Purchase #3 $191.72   5.863%   $202.9605   $202.96   $202.95   $203.00  
  Purchase #4 $31.74   8.703%   $34.5023   $34.50   $34.50   $34.50  
  Purchase #5 $137.74   7.103%   $147.5237   $147.52   $147.50   $147.50  
  Purchase #6 $41.89   12.440%   $47.1011   $47.10   $47.10   $47.10  
  Purchase #7 $233.49   12.173%   $261.9127   $261.91   $261.90   $261.90  
  7 purchase totals = $811.15       $886.6099   $886.60   $886.55   $886.60