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 $167.50   8.680%   $182.039   $182.04   $182.05   $182.00  
  Purchase #2 $250.98   13.835%   $285.7031   $285.70   $285.70   $285.70  
  Purchase #3 $213.82   10.169%   $235.5634   $235.56   $235.55   $235.60  
  Purchase #4 $171.72   7.539%   $184.666   $184.67   $184.65   $184.70  
  Purchase #5 $230.48   12.765%   $259.9008   $259.90   $259.90   $259.90  
  Purchase #6 $224.78   11.176%   $249.9014   $249.90   $249.90   $249.90  
  Purchase #7 $204.88   6.863%   $218.9409   $218.94   $218.95   $218.90  
  7 purchase totals = $1,464.16       $1,616.7146   $1,616.71   $1,616.70   $1,616.70