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 $208.58   13.292%   $236.3045   $236.30   $236.30   $236.30  
  Purchase #2 $13.36   11.640%   $14.9151   $14.92   $14.90   $14.90  
  Purchase #3 $183.29   8.525%   $198.9155   $198.92   $198.90   $198.90  
  Purchase #4 $63.96   5.212%   $67.2936   $67.29   $67.30   $67.30  
  Purchase #5 $31.46   7.109%   $33.6965   $33.70   $33.70   $33.70  
  Purchase #6 $160.53   4.774%   $168.1937   $168.19   $168.20   $168.20  
  Purchase #7 $152.61   9.515%   $167.1308   $167.13   $167.15   $167.10  
  7 purchase totals = $813.79       $886.4497   $886.45   $886.45   $886.40