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 $134.48   12.348%   $151.0856   $151.09   $151.10   $151.10  
  Purchase #2 $226.88   6.383%   $241.3618   $241.36   $241.35   $241.40  
  Purchase #3 $157.45   6.458%   $167.6181   $167.62   $167.60   $167.60  
  Purchase #4 $208.36   6.145%   $221.1637   $221.16   $221.15   $221.20  
  Purchase #5 $134.51   12.626%   $151.4932   $151.49   $151.50   $151.50  
  Purchase #6 $239.78   4.662%   $250.9585   $250.96   $250.95   $251.00  
  Purchase #7 $8.91   7.457%   $9.5744   $9.57   $9.55   $9.60  
  7 purchase totals = $1,110.37       $1,193.2553   $1,193.25   $1,193.20   $1,193.40