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 $53.53   12.663%   $60.3085   $60.31   $60.30   $60.30  
  Purchase #2 $242.57   12.354%   $272.5371   $272.54   $272.55   $272.50  
  Purchase #3 $163.39   3.131%   $168.5057   $168.51   $168.50   $168.50  
  Purchase #4 $187.53   12.195%   $210.3993   $210.40   $210.40   $210.40  
  Purchase #5 $73.26   13.690%   $83.2893   $83.29   $83.30   $83.30  
  Purchase #6 $186.44   3.461%   $192.8927   $192.89   $192.90   $192.90  
  Purchase #7 $213.86   5.292%   $225.1775   $225.18   $225.20   $225.20  
  7 purchase totals = $1,120.58       $1,213.1101   $1,213.12   $1,213.15   $1,213.10