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 $53.32   13.607%   $60.5753   $60.58   $60.60   $60.60  
  Purchase #2 $121.84   3.170%   $125.7023   $125.70   $125.70   $125.70  
  Purchase #3 $18.68   3.284%   $19.2935   $19.29   $19.30   $19.30  
  Purchase #4 $155.47   11.392%   $173.1811   $173.18   $173.20   $173.20  
  Purchase #5 $157.74   8.712%   $171.4823   $171.48   $171.50   $171.50  
  Purchase #6 $120.42   4.745%   $126.1339   $126.13   $126.15   $126.10  
  Purchase #7 $40.97   13.661%   $46.5669   $46.57   $46.55   $46.60  
  7 purchase totals = $668.44       $722.9353   $722.93   $723.00   $723.00