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 $81.76   13.816%   $93.056   $93.06   $93.05   $93.10  
  Purchase #2 $148.35   13.412%   $168.2467   $168.25   $168.25   $168.20  
  Purchase #3 $91.25   11.405%   $101.6571   $101.66   $101.65   $101.70  
  Purchase #4 $233.71   6.167%   $248.1229   $248.12   $248.10   $248.10  
  Purchase #5 $147.90   13.501%   $167.868   $167.87   $167.85   $167.90  
  Purchase #6 $248.51   13.503%   $282.0663   $282.07   $282.05   $282.10  
  Purchase #7 $120.63   4.702%   $126.302   $126.30   $126.30   $126.30  
  7 purchase totals = $1,072.11       $1,187.3190   $1,187.33   $1,187.25   $1,187.40