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 $63.90   6.701%   $68.1819   $68.18   $68.20   $68.20  
  Purchase #2 $230.40   5.319%   $242.655   $242.66   $242.65   $242.70  
  Purchase #3 $35.36   9.158%   $38.5983   $38.60   $38.60   $38.60  
  Purchase #4 $91.25   3.296%   $94.2576   $94.26   $94.25   $94.30  
  Purchase #5 $162.58   3.529%   $168.3174   $168.32   $168.30   $168.30  
  Purchase #6 $231.80   13.760%   $263.6957   $263.70   $263.70   $263.70  
  Purchase #7 $66.93   9.577%   $73.3399   $73.34   $73.35   $73.30  
  7 purchase totals = $882.22       $949.0458   $949.06   $949.05   $949.10