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 $244.38   8.855%   $266.0198   $266.02   $266.00   $266.00  
  Purchase #2 $200.96   4.114%   $209.2275   $209.23   $209.25   $209.20  
  Purchase #3 $15.29   12.295%   $17.1699   $17.17   $17.15   $17.20  
  Purchase #4 $220.44   9.261%   $240.8549   $240.85   $240.85   $240.90  
  Purchase #5 $115.40   4.622%   $120.7338   $120.73   $120.75   $120.70  
  Purchase #6 $72.62   6.698%   $77.4841   $77.48   $77.50   $77.50  
  Purchase #7 $202.48   6.387%   $215.4124   $215.41   $215.40   $215.40  
  7 purchase totals = $1,071.57       $1,146.9024   $1,146.89   $1,146.90   $1,146.90