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 $207.94   13.573%   $236.1637   $236.16   $236.15   $236.20  
  Purchase #2 $167.53   4.303%   $174.7388   $174.74   $174.75   $174.70  
  Purchase #3 $246.41   13.221%   $278.9879   $278.99   $279.00   $279.00  
  Purchase #4 $76.69   6.784%   $81.8926   $81.89   $81.90   $81.90  
  Purchase #5 $114.26   11.697%   $127.625   $127.63   $127.65   $127.60  
  Purchase #6 $32.33   3.181%   $33.3584   $33.36   $33.35   $33.40  
  Purchase #7 $161.42   4.199%   $168.198   $168.20   $168.20   $168.20  
  7 purchase totals = $1,006.58       $1,100.9644   $1,100.97   $1,101.00   $1,101.00