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 $66.94   4.204%   $69.7542   $69.75   $69.75   $69.80  
  Purchase #2 $63.25   3.838%   $65.6775   $65.68   $65.70   $65.70  
  Purchase #3 $186.97   3.652%   $193.7981   $193.80   $193.80   $193.80  
  Purchase #4 $19.34   8.156%   $20.9174   $20.92   $20.90   $20.90  
  Purchase #5 $67.62   5.265%   $71.1802   $71.18   $71.20   $71.20  
  Purchase #6 $200.67   3.270%   $207.2319   $207.23   $207.25   $207.20  
  Purchase #7 $45.99   3.636%   $47.6622   $47.66   $47.65   $47.70  
  7 purchase totals = $650.78       $676.2215   $676.22   $676.25   $676.30