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 $92.35   6.869%   $98.6935   $98.69   $98.70   $98.70  
  Purchase #2 $157.53   6.361%   $167.5505   $167.55   $167.55   $167.60  
  Purchase #3 $22.75   6.533%   $24.2363   $24.24   $24.25   $24.20  
  Purchase #4 $172.37   11.138%   $191.5686   $191.57   $191.55   $191.60  
  Purchase #5 $146.41   3.162%   $151.0395   $151.04   $151.05   $151.00  
  Purchase #6 $32.26   11.324%   $35.9131   $35.91   $35.90   $35.90  
  Purchase #7 $31.73   11.599%   $35.4104   $35.41   $35.40   $35.40  
  7 purchase totals = $655.40       $704.4119   $704.41   $704.40   $704.40