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 $42.36   9.161%   $46.2406   $46.24   $46.25   $46.20  
  Purchase #2 $158.57   6.408%   $168.7312   $168.73   $168.75   $168.70  
  Purchase #3 $187.73   11.835%   $209.9478   $209.95   $209.95   $209.90  
  Purchase #4 $30.77   10.701%   $34.0627   $34.06   $34.05   $34.10  
  Purchase #5 $163.74   11.277%   $182.205   $182.21   $182.20   $182.20  
  Purchase #6 $96.74   12.721%   $109.0463   $109.05   $109.05   $109.00  
  Purchase #7 $13.44   8.452%   $14.5759   $14.58   $14.60   $14.60  
  7 purchase totals = $693.35       $764.8095   $764.82   $764.85   $764.70