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 $246.97   7.703%   $265.9941   $265.99   $266.00   $266.00  
  Purchase #2 $59.50   11.856%   $66.5543   $66.55   $66.55   $66.60  
  Purchase #3 $199.47   13.813%   $227.0228   $227.02   $227.00   $227.00  
  Purchase #4 $192.26   3.208%   $198.4277   $198.43   $198.45   $198.40  
  Purchase #5 $160.50   13.490%   $182.1515   $182.15   $182.15   $182.20  
  Purchase #6 $27.28   7.589%   $29.3503   $29.35   $29.35   $29.40  
  Purchase #7 $190.67   12.474%   $214.4542   $214.45   $214.45   $214.50  
  7 purchase totals = $1,076.65       $1,183.9549   $1,183.94   $1,183.95   $1,184.10