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 $242.57   13.374%   $275.0113   $275.01   $275.00   $275.00  
  Purchase #2 $137.62   6.450%   $146.4965   $146.50   $146.50   $146.50  
  Purchase #3 $44.85   13.623%   $50.9599   $50.96   $50.95   $51.00  
  Purchase #4 $119.38   6.603%   $127.2627   $127.26   $127.25   $127.30  
  Purchase #5 $182.71   10.428%   $201.763   $201.76   $201.75   $201.80  
  Purchase #6 $137.76   7.126%   $147.5768   $147.58   $147.60   $147.60  
  Purchase #7 $181.70   8.531%   $197.2008   $197.20   $197.20   $197.20  
  7 purchase totals = $1,046.59       $1,146.2710   $1,146.27   $1,146.25   $1,146.40