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 $87.73   12.176%   $98.412   $98.41   $98.40   $98.40  
  Purchase #2 $245.84   9.397%   $268.9416   $268.94   $268.95   $268.90  
  Purchase #3 $192.39   10.226%   $212.0638   $212.06   $212.05   $212.10  
  Purchase #4 $239.95   6.659%   $255.9283   $255.93   $255.95   $255.90  
  Purchase #5 $142.71   11.164%   $158.6421   $158.64   $158.65   $158.60  
  Purchase #6 $84.62   13.440%   $95.9929   $95.99   $96.00   $96.00  
  Purchase #7 $218.73   10.186%   $241.0098   $241.01   $241.00   $241.00  
  7 purchase totals = $1,211.97       $1,330.9905   $1,330.98   $1,331.00   $1,330.90