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 $176.28   9.619%   $193.2364   $193.24   $193.25   $193.20  
  Purchase #2 $22.92   4.728%   $24.0037   $24.00   $24.00   $24.00  
  Purchase #3 $245.63   7.466%   $263.9687   $263.97   $263.95   $264.00  
  Purchase #4 $182.96   5.835%   $193.6357   $193.64   $193.65   $193.60  
  Purchase #5 $133.33   9.236%   $145.6444   $145.64   $145.65   $145.60  
  Purchase #6 $175.91   10.783%   $194.8784   $194.88   $194.90   $194.90  
  Purchase #7 $246.83   11.448%   $275.0871   $275.09   $275.10   $275.10  
  7 purchase totals = $1,183.86       $1,290.4544   $1,290.46   $1,290.50   $1,290.40