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 $194.59   3.651%   $201.6945   $201.69   $201.70   $201.70  
  Purchase #2 $247.35   7.778%   $266.5889   $266.59   $266.60   $266.60  
  Purchase #3 $114.76   5.341%   $120.8893   $120.89   $120.90   $120.90  
  Purchase #4 $51.27   9.530%   $56.156   $56.16   $56.15   $56.20  
  Purchase #5 $68.62   4.470%   $71.6873   $71.69   $71.70   $71.70  
  Purchase #6 $76.53   10.770%   $84.7723   $84.77   $84.75   $84.80  
  Purchase #7 $175.69   11.130%   $195.2443   $195.24   $195.25   $195.20  
  7 purchase totals = $928.81       $997.0326   $997.03   $997.05   $997.10