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 $84.78   13.244%   $96.0083   $96.01   $96.00   $96.00  
  Purchase #2 $58.51   10.351%   $64.5664   $64.57   $64.55   $64.60  
  Purchase #3 $31.56   12.248%   $35.4255   $35.43   $35.45   $35.40  
  Purchase #4 $63.53   7.152%   $68.0737   $68.07   $68.05   $68.10  
  Purchase #5 $124.38   3.335%   $128.5281   $128.53   $128.55   $128.50  
  Purchase #6 $34.32   8.316%   $37.1741   $37.17   $37.15   $37.20  
  Purchase #7 $220.35   10.147%   $242.7089   $242.71   $242.70   $242.70  
  7 purchase totals = $617.43       $672.4850   $672.49   $672.45   $672.50