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 $196.76   3.186%   $203.0288   $203.03   $203.05   $203.00  
  Purchase #2 $151.36   7.797%   $163.1615   $163.16   $163.15   $163.20  
  Purchase #3 $240.76   3.734%   $249.75   $249.75   $249.75   $249.80  
  Purchase #4 $194.48   9.394%   $212.7495   $212.75   $212.75   $212.70  
  Purchase #5 $61.51   5.128%   $64.6642   $64.66   $64.65   $64.70  
  Purchase #6 $112.45   5.334%   $118.4481   $118.45   $118.45   $118.40  
  Purchase #7 $214.35   11.536%   $239.0774   $239.08   $239.10   $239.10  
  7 purchase totals = $1,171.67       $1,250.8795   $1,250.88   $1,250.90   $1,250.90