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 $156.81   12.756%   $176.8127   $176.81   $176.80   $176.80  
  Purchase #2 $126.84   13.204%   $143.588   $143.59   $143.60   $143.60  
  Purchase #3 $50.92   11.114%   $56.5792   $56.58   $56.60   $56.60  
  Purchase #4 $96.66   4.658%   $101.1624   $101.16   $101.15   $101.20  
  Purchase #5 $237.26   6.243%   $252.0721   $252.07   $252.05   $252.10  
  Purchase #6 $68.41   11.466%   $76.2539   $76.25   $76.25   $76.30  
  Purchase #7 $19.59   4.133%   $20.3997   $20.40   $20.40   $20.40  
  7 purchase totals = $756.49       $826.8680   $826.86   $826.85   $827.00