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 $206.86   11.168%   $229.9621   $229.96   $229.95   $230.00  
  Purchase #2 $23.25   8.874%   $25.3132   $25.31   $25.30   $25.30  
  Purchase #3 $215.29   4.533%   $225.0491   $225.05   $225.05   $225.00  
  Purchase #4 $32.60   12.127%   $36.5534   $36.55   $36.55   $36.60  
  Purchase #5 $232.53   12.725%   $262.1194   $262.12   $262.10   $262.10  
  Purchase #6 $240.91   10.801%   $266.9307   $266.93   $266.95   $266.90  
  Purchase #7 $228.62   9.665%   $250.7161   $250.72   $250.70   $250.70  
  7 purchase totals = $1,180.06       $1,296.6440   $1,296.64   $1,296.60   $1,296.60