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 $214.46   11.689%   $239.5282   $239.53   $239.55   $239.50  
  Purchase #2 $172.48   11.817%   $192.862   $192.86   $192.85   $192.90  
  Purchase #3 $52.47   5.388%   $55.2971   $55.30   $55.30   $55.30  
  Purchase #4 $211.76   5.325%   $223.0362   $223.04   $223.05   $223.00  
  Purchase #5 $206.40   9.530%   $226.0699   $226.07   $226.05   $226.10  
  Purchase #6 $200.92   3.167%   $207.2831   $207.28   $207.30   $207.30  
  Purchase #7 $162.48   10.547%   $179.6168   $179.62   $179.60   $179.60  
  7 purchase totals = $1,220.97       $1,323.6933   $1,323.70   $1,323.70   $1,323.70