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 $23.98   6.813%   $25.6138   $25.61   $25.60   $25.60  
  Purchase #2 $68.63   4.389%   $71.6422   $71.64   $71.65   $71.60  
  Purchase #3 $159.95   12.493%   $179.9326   $179.93   $179.95   $179.90  
  Purchase #4 $216.55   3.590%   $224.3241   $224.32   $224.30   $224.30  
  Purchase #5 $223.50   10.172%   $246.2344   $246.23   $246.25   $246.20  
  Purchase #6 $183.55   4.752%   $192.2723   $192.27   $192.25   $192.30  
  Purchase #7 $121.53   4.438%   $126.9235   $126.92   $126.90   $126.90  
  7 purchase totals = $997.69       $1,066.9429   $1,066.92   $1,066.90   $1,066.80