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 $86.87   9.714%   $95.3086   $95.31   $95.30   $95.30  
  Purchase #2 $164.98   13.414%   $187.1104   $187.11   $187.10   $187.10  
  Purchase #3 $143.62   8.479%   $155.7975   $155.80   $155.80   $155.80  
  Purchase #4 $61.80   3.326%   $63.8555   $63.86   $63.85   $63.90  
  Purchase #5 $33.94   8.126%   $36.698   $36.70   $36.70   $36.70  
  Purchase #6 $119.29   10.570%   $131.899   $131.90   $131.90   $131.90  
  Purchase #7 $118.94   13.696%   $135.23   $135.23   $135.25   $135.20  
  7 purchase totals = $729.44       $805.8990   $805.91   $805.90   $805.90