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 $34.68   10.551%   $38.3391   $38.34   $38.35   $38.30  
  Purchase #2 $61.39   4.309%   $64.0353   $64.04   $64.05   $64.00  
  Purchase #3 $187.59   4.441%   $195.9209   $195.92   $195.90   $195.90  
  Purchase #4 $190.62   5.779%   $201.6359   $201.64   $201.65   $201.60  
  Purchase #5 $44.72   5.765%   $47.2981   $47.30   $47.30   $47.30  
  Purchase #6 $215.55   8.329%   $233.5032   $233.50   $233.50   $233.50  
  Purchase #7 $62.25   7.793%   $67.1011   $67.10   $67.10   $67.10  
  7 purchase totals = $796.80       $847.8336   $847.84   $847.85   $847.70