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 $238.43   8.745%   $259.2807   $259.28   $259.30   $259.30  
  Purchase #2 $221.97   12.721%   $250.2068   $250.21   $250.20   $250.20  
  Purchase #3 $86.28   9.641%   $94.5983   $94.60   $94.60   $94.60  
  Purchase #4 $148.76   11.686%   $166.1441   $166.14   $166.15   $166.10  
  Purchase #5 $87.57   4.130%   $91.1866   $91.19   $91.20   $91.20  
  Purchase #6 $228.89   5.351%   $241.1379   $241.14   $241.15   $241.10  
  Purchase #7 $235.65   13.110%   $266.5437   $266.54   $266.55   $266.50  
  7 purchase totals = $1,247.55       $1,369.0981   $1,369.10   $1,369.15   $1,369.00