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 $198.26   9.335%   $216.7676   $216.77   $216.75   $216.80  
  Purchase #2 $153.28   4.597%   $160.3263   $160.33   $160.35   $160.30  
  Purchase #3 $244.99   11.286%   $272.6396   $272.64   $272.65   $272.60  
  Purchase #4 $183.44   6.274%   $194.949   $194.95   $194.95   $194.90  
  Purchase #5 $171.36   5.790%   $181.2817   $181.28   $181.30   $181.30  
  Purchase #6 $126.58   3.358%   $130.8306   $130.83   $130.85   $130.80  
  Purchase #7 $199.46   4.519%   $208.4736   $208.47   $208.45   $208.50  
  7 purchase totals = $1,277.37       $1,365.2684   $1,365.27   $1,365.30   $1,365.20