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 $214.84   3.799%   $223.0018   $223.00   $223.00   $223.00  
  Purchase #2 $191.88   8.683%   $208.5409   $208.54   $208.55   $208.50  
  Purchase #3 $38.29   3.824%   $39.7542   $39.75   $39.75   $39.80  
  Purchase #4 $119.94   7.117%   $128.4761   $128.48   $128.50   $128.50  
  Purchase #5 $5.67   6.475%   $6.0371   $6.04   $6.05   $6.00  
  Purchase #6 $48.41   12.311%   $54.3698   $54.37   $54.35   $54.40  
  Purchase #7 $250.42   6.563%   $266.8551   $266.86   $266.85   $266.90  
  7 purchase totals = $869.45       $927.0350   $927.04   $927.05   $927.10