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 $241.72   11.287%   $269.0029   $269.00   $269.00   $269.00  
  Purchase #2 $108.48   6.793%   $115.849   $115.85   $115.85   $115.80  
  Purchase #3 $156.56   7.310%   $168.0045   $168.00   $168.00   $168.00  
  Purchase #4 $195.70   11.713%   $218.6223   $218.62   $218.60   $218.60  
  Purchase #5 $125.76   6.683%   $134.1645   $134.16   $134.15   $134.20  
  Purchase #6 $167.46   8.744%   $182.1027   $182.10   $182.10   $182.10  
  Purchase #7 $86.97   8.819%   $94.6399   $94.64   $94.65   $94.60  
  7 purchase totals = $1,082.65       $1,182.3858   $1,182.37   $1,182.35   $1,182.30