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 $175.32   10.361%   $193.4849   $193.48   $193.50   $193.50  
  Purchase #2 $78.48   12.653%   $88.4101   $88.41   $88.40   $88.40  
  Purchase #3 $186.62   13.549%   $211.9051   $211.91   $211.90   $211.90  
  Purchase #4 $249.70   8.420%   $270.7247   $270.72   $270.70   $270.70  
  Purchase #5 $113.42   11.752%   $126.7491   $126.75   $126.75   $126.70  
  Purchase #6 $89.93   3.428%   $93.0128   $93.01   $93.00   $93.00  
  Purchase #7 $34.51   10.105%   $37.9972   $38.00   $38.00   $38.00  
  7 purchase totals = $927.98       $1,022.2839   $1,022.28   $1,022.25   $1,022.20