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 $120.85   12.794%   $136.3115   $136.31   $136.30   $136.30  
  Purchase #2 $240.38   4.294%   $250.7019   $250.70   $250.70   $250.70  
  Purchase #3 $24.67   11.833%   $27.5892   $27.59   $27.60   $27.60  
  Purchase #4 $241.86   5.461%   $255.068   $255.07   $255.05   $255.10  
  Purchase #5 $173.81   11.753%   $194.2379   $194.24   $194.25   $194.20  
  Purchase #6 $83.28   11.230%   $92.6323   $92.63   $92.65   $92.60  
  Purchase #7 $143.25   7.483%   $153.9694   $153.97   $153.95   $154.00  
  7 purchase totals = $1,028.10       $1,110.5102   $1,110.51   $1,110.50   $1,110.50