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 $82.51   11.802%   $92.2478   $92.25   $92.25   $92.20  
  Purchase #2 $135.39   3.452%   $140.0637   $140.06   $140.05   $140.10  
  Purchase #3 $98.93   7.497%   $106.3468   $106.35   $106.35   $106.30  
  Purchase #4 $231.85   4.766%   $242.9   $242.90   $242.90   $242.90  
  Purchase #5 $24.61   10.701%   $27.2435   $27.24   $27.25   $27.20  
  Purchase #6 $115.76   5.453%   $122.0724   $122.07   $122.05   $122.10  
  Purchase #7 $70.86   5.582%   $74.8154   $74.82   $74.80   $74.80  
  7 purchase totals = $759.91       $805.6896   $805.69   $805.65   $805.60