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 $198.87   13.653%   $226.0217   $226.02   $226.00   $226.00  
  Purchase #2 $211.58   10.655%   $234.1238   $234.12   $234.10   $234.10  
  Purchase #3 $24.36   3.654%   $25.2501   $25.25   $25.25   $25.30  
  Purchase #4 $206.61   9.162%   $225.5396   $225.54   $225.55   $225.50  
  Purchase #5 $183.73   13.339%   $208.2377   $208.24   $208.25   $208.20  
  Purchase #6 $60.62   13.567%   $68.8443   $68.84   $68.85   $68.80  
  Purchase #7 $235.34   9.836%   $258.488   $258.49   $258.50   $258.50  
  7 purchase totals = $1,121.11       $1,246.5052   $1,246.50   $1,246.50   $1,246.40