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 $216.41   12.726%   $243.9503   $243.95   $243.95   $244.00  
  Purchase #2 $177.94   9.721%   $195.2375   $195.24   $195.25   $195.20  
  Purchase #3 $58.86   10.760%   $65.1933   $65.19   $65.20   $65.20  
  Purchase #4 $49.68   3.522%   $51.4297   $51.43   $51.45   $51.40  
  Purchase #5 $196.45   7.851%   $211.8733   $211.87   $211.85   $211.90  
  Purchase #6 $247.62   7.761%   $266.8378   $266.84   $266.85   $266.80  
  Purchase #7 $236.53   6.770%   $252.5431   $252.54   $252.55   $252.50  
  7 purchase totals = $1,183.49       $1,287.0650   $1,287.06   $1,287.10   $1,287.00