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 $242.86   13.811%   $276.4014   $276.40   $276.40   $276.40  
  Purchase #2 $140.84   9.659%   $154.4437   $154.44   $154.45   $154.40  
  Purchase #3 $145.27   7.363%   $155.9662   $155.97   $155.95   $156.00  
  Purchase #4 $97.98   7.396%   $105.2266   $105.23   $105.25   $105.20  
  Purchase #5 $207.73   13.864%   $236.5297   $236.53   $236.55   $236.50  
  Purchase #6 $21.41   12.585%   $24.1044   $24.10   $24.10   $24.10  
  Purchase #7 $214.98   7.420%   $230.9315   $230.93   $230.95   $230.90  
  7 purchase totals = $1,071.07       $1,183.6035   $1,183.60   $1,183.65   $1,183.50