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 $74.96   10.775%   $83.0369   $83.04   $83.05   $83.00  
  Purchase #2 $249.48   6.493%   $265.6787   $265.68   $265.70   $265.70  
  Purchase #3 $173.65   8.636%   $188.6464   $188.65   $188.65   $188.60  
  Purchase #4 $152.52   6.299%   $162.1272   $162.13   $162.15   $162.10  
  Purchase #5 $89.80   11.804%   $100.4   $100.40   $100.40   $100.40  
  Purchase #6 $176.87   4.676%   $185.1404   $185.14   $185.15   $185.10  
  Purchase #7 $244.27   8.569%   $265.2015   $265.20   $265.20   $265.20  
  7 purchase totals = $1,161.55       $1,250.2311   $1,250.24   $1,250.30   $1,250.10