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 $125.65   13.265%   $142.3175   $142.32   $142.30   $142.30  
  Purchase #2 $182.87   7.822%   $197.1741   $197.17   $197.15   $197.20  
  Purchase #3 $62.52   7.675%   $67.3184   $67.32   $67.30   $67.30  
  Purchase #4 $196.96   4.236%   $205.3032   $205.30   $205.30   $205.30  
  Purchase #5 $191.64   9.708%   $210.2444   $210.24   $210.25   $210.20  
  Purchase #6 $166.99   7.575%   $179.6395   $179.64   $179.65   $179.60  
  Purchase #7 $55.76   4.432%   $58.2313   $58.23   $58.25   $58.20  
  7 purchase totals = $982.39       $1,060.2284   $1,060.22   $1,060.20   $1,060.10