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 $168.85   4.230%   $175.9924   $175.99   $176.00   $176.00  
  Purchase #2 $248.72   13.164%   $281.4615   $281.46   $281.45   $281.50  
  Purchase #3 $21.56   10.493%   $23.8223   $23.82   $23.80   $23.80  
  Purchase #4 $98.36   7.261%   $105.5019   $105.50   $105.50   $105.50  
  Purchase #5 $211.47   3.668%   $219.2267   $219.23   $219.25   $219.20  
  Purchase #6 $68.78   7.507%   $73.9433   $73.94   $73.95   $73.90  
  Purchase #7 $65.96   13.640%   $74.9569   $74.96   $74.95   $75.00  
  7 purchase totals = $883.70       $954.9050   $954.90   $954.90   $954.90