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 $71.38   6.310%   $75.8841   $75.88   $75.90   $75.90  
  Purchase #2 $119.54   5.845%   $126.5271   $126.53   $126.55   $126.50  
  Purchase #3 $50.45   6.641%   $53.8004   $53.80   $53.80   $53.80  
  Purchase #4 $210.30   7.747%   $226.5919   $226.59   $226.60   $226.60  
  Purchase #5 $51.87   12.868%   $58.5446   $58.54   $58.55   $58.50  
  Purchase #6 $46.80   8.297%   $50.683   $50.68   $50.70   $50.70  
  Purchase #7 $195.99   11.433%   $218.3975   $218.40   $218.40   $218.40  
  7 purchase totals = $746.33       $810.4286   $810.42   $810.50   $810.40