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 $208.93   11.718%   $233.4124   $233.41   $233.40   $233.40  
  Purchase #2 $114.70   10.739%   $127.0176   $127.02   $127.00   $127.00  
  Purchase #3 $158.95   5.428%   $167.5778   $167.58   $167.60   $167.60  
  Purchase #4 $183.35   5.351%   $193.1611   $193.16   $193.15   $193.20  
  Purchase #5 $206.40   13.500%   $234.264   $234.26   $234.25   $234.30  
  Purchase #6 $55.64   11.651%   $62.1226   $62.12   $62.10   $62.10  
  Purchase #7 $59.65   7.313%   $64.0122   $64.01   $64.00   $64.00  
  7 purchase totals = $987.62       $1,081.5677   $1,081.56   $1,081.50   $1,081.60