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 $203.36   6.712%   $217.0095   $217.01   $217.00   $217.00  
  Purchase #2 $162.40   7.724%   $174.9438   $174.94   $174.95   $174.90  
  Purchase #3 $78.77   6.528%   $83.9121   $83.91   $83.90   $83.90  
  Purchase #4 $29.38   4.681%   $30.7553   $30.76   $30.75   $30.80  
  Purchase #5 $209.97   10.831%   $232.7119   $232.71   $232.70   $232.70  
  Purchase #6 $95.91   9.475%   $104.9975   $105.00   $105.00   $105.00  
  Purchase #7 $212.91   8.403%   $230.8008   $230.80   $230.80   $230.80  
  7 purchase totals = $992.70       $1,075.1309   $1,075.13   $1,075.10   $1,075.10