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 $22.96   13.421%   $26.0415   $26.04   $26.05   $26.00  
  Purchase #2 $92.25   6.727%   $98.4557   $98.46   $98.45   $98.50  
  Purchase #3 $100.29   12.263%   $112.5886   $112.59   $112.60   $112.60  
  Purchase #4 $173.51   13.666%   $197.2219   $197.22   $197.20   $197.20  
  Purchase #5 $156.69   7.704%   $168.7614   $168.76   $168.75   $168.80  
  Purchase #6 $221.62   5.120%   $232.9669   $232.97   $232.95   $233.00  
  Purchase #7 $223.92   3.392%   $231.5154   $231.52   $231.50   $231.50  
  7 purchase totals = $991.24       $1,067.5514   $1,067.56   $1,067.50   $1,067.60