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 $157.96   10.336%   $174.2867   $174.29   $174.30   $174.30  
  Purchase #2 $218.32   8.423%   $236.7091   $236.71   $236.70   $236.70  
  Purchase #3 $220.49   5.793%   $233.263   $233.26   $233.25   $233.30  
  Purchase #4 $75.36   13.762%   $85.731   $85.73   $85.75   $85.70  
  Purchase #5 $233.47   9.871%   $256.5158   $256.52   $256.50   $256.50  
  Purchase #6 $131.36   7.624%   $141.3749   $141.37   $141.35   $141.40  
  Purchase #7 $178.41   3.757%   $185.1129   $185.11   $185.10   $185.10  
  7 purchase totals = $1,215.37       $1,312.9934   $1,312.99   $1,312.95   $1,313.00