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 $207.57   10.519%   $229.4043   $229.40   $229.40   $229.40  
  Purchase #2 $63.41   7.480%   $68.1531   $68.15   $68.15   $68.20  
  Purchase #3 $88.34   7.115%   $94.6254   $94.63   $94.65   $94.60  
  Purchase #4 $95.27   11.670%   $106.388   $106.39   $106.40   $106.40  
  Purchase #5 $238.97   11.423%   $266.2675   $266.27   $266.25   $266.30  
  Purchase #6 $235.72   11.381%   $262.5473   $262.55   $262.55   $262.50  
  Purchase #7 $94.39   6.246%   $100.2856   $100.29   $100.30   $100.30  
  7 purchase totals = $1,023.67       $1,127.6712   $1,127.68   $1,127.70   $1,127.70