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 $58.30   8.647%   $63.3412   $63.34   $63.35   $63.30  
  Purchase #2 $18.74   4.388%   $19.5623   $19.56   $19.55   $19.60  
  Purchase #3 $206.60   5.560%   $218.087   $218.09   $218.10   $218.10  
  Purchase #4 $32.57   12.146%   $36.526   $36.53   $36.55   $36.50  
  Purchase #5 $160.25   5.286%   $168.7208   $168.72   $168.70   $168.70  
  Purchase #6 $72.86   6.449%   $77.5587   $77.56   $77.55   $77.60  
  Purchase #7 $142.63   6.250%   $151.5444   $151.54   $151.55   $151.50  
  7 purchase totals = $691.95       $735.3404   $735.34   $735.35   $735.30