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 $138.33   5.862%   $146.4389   $146.44   $146.45   $146.40  
  Purchase #2 $86.93   7.669%   $93.5967   $93.60   $93.60   $93.60  
  Purchase #3 $101.46   10.684%   $112.3   $112.30   $112.30   $112.30  
  Purchase #4 $230.36   8.206%   $249.2633   $249.26   $249.25   $249.30  
  Purchase #5 $247.65   4.532%   $258.8735   $258.87   $258.85   $258.90  
  Purchase #6 $69.44   5.130%   $73.0023   $73.00   $73.00   $73.00  
  Purchase #7 $204.88   10.595%   $226.587   $226.59   $226.60   $226.60  
  7 purchase totals = $1,079.05       $1,160.0617   $1,160.06   $1,160.05   $1,160.10