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 $189.27   3.510%   $195.9134   $195.91   $195.90   $195.90  
  Purchase #2 $172.45   9.358%   $188.5879   $188.59   $188.60   $188.60  
  Purchase #3 $208.98   13.167%   $236.4964   $236.50   $236.50   $236.50  
  Purchase #4 $32.73   8.652%   $35.5618   $35.56   $35.55   $35.60  
  Purchase #5 $110.45   4.218%   $115.1088   $115.11   $115.10   $115.10  
  Purchase #6 $187.70   4.409%   $195.9757   $195.98   $196.00   $196.00  
  Purchase #7 $92.66   7.862%   $99.9449   $99.94   $99.95   $99.90  
  7 purchase totals = $994.24       $1,067.5889   $1,067.59   $1,067.60   $1,067.60