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 $64.26   6.682%   $68.5539   $68.55   $68.55   $68.60  
  Purchase #2 $93.41   3.358%   $96.5467   $96.55   $96.55   $96.50  
  Purchase #3 $199.36   6.463%   $212.2446   $212.24   $212.25   $212.20  
  Purchase #4 $113.93   9.274%   $124.4959   $124.50   $124.50   $124.50  
  Purchase #5 $123.36   11.619%   $137.6932   $137.69   $137.70   $137.70  
  Purchase #6 $168.67   5.689%   $178.2656   $178.27   $178.25   $178.30  
  Purchase #7 $111.55   10.327%   $123.0698   $123.07   $123.05   $123.10  
  7 purchase totals = $874.54       $940.8697   $940.87   $940.85   $940.90