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 $239.62   11.458%   $267.0757   $267.08   $267.10   $267.10  
  Purchase #2 $72.42   3.780%   $75.1575   $75.16   $75.15   $75.20  
  Purchase #3 $61.76   10.863%   $68.469   $68.47   $68.45   $68.50  
  Purchase #4 $163.73   7.191%   $175.5038   $175.50   $175.50   $175.50  
  Purchase #5 $154.60   11.852%   $172.9232   $172.92   $172.90   $172.90  
  Purchase #6 $182.39   7.731%   $196.4906   $196.49   $196.50   $196.50  
  Purchase #7 $46.78   9.470%   $51.2101   $51.21   $51.20   $51.20  
  7 purchase totals = $921.30       $1,006.8299   $1,006.83   $1,006.80   $1,006.90