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 $68.82   6.474%   $73.2754   $73.28   $73.30   $73.30  
  Purchase #2 $171.88   11.695%   $191.9814   $191.98   $192.00   $192.00  
  Purchase #3 $144.78   8.772%   $157.4801   $157.48   $157.50   $157.50  
  Purchase #4 $110.36   3.669%   $114.4091   $114.41   $114.40   $114.40  
  Purchase #5 $55.37   9.217%   $60.4735   $60.47   $60.45   $60.50  
  Purchase #6 $147.85   13.727%   $168.1454   $168.15   $168.15   $168.10  
  Purchase #7 $245.93   4.218%   $256.3033   $256.30   $256.30   $256.30  
  7 purchase totals = $944.99       $1,022.0682   $1,022.07   $1,022.10   $1,022.10