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 $148.63   12.790%   $167.6398   $167.64   $167.65   $167.60  
  Purchase #2 $215.84   8.276%   $233.7029   $233.70   $233.70   $233.70  
  Purchase #3 $52.77   8.206%   $57.1003   $57.10   $57.10   $57.10  
  Purchase #4 $91.37   8.798%   $99.4087   $99.41   $99.40   $99.40  
  Purchase #5 $20.94   9.699%   $22.971   $22.97   $22.95   $23.00  
  Purchase #6 $123.50   9.514%   $135.2498   $135.25   $135.25   $135.20  
  Purchase #7 $76.70   5.440%   $80.8725   $80.87   $80.85   $80.90  
  7 purchase totals = $729.75       $796.9450   $796.94   $796.90   $796.90