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 $242.80   4.211%   $253.0243   $253.02   $253.00   $253.00  
  Purchase #2 $232.85   4.686%   $243.7614   $243.76   $243.75   $243.80  
  Purchase #3 $76.90   5.288%   $80.9665   $80.97   $80.95   $81.00  
  Purchase #4 $206.82   3.124%   $213.2811   $213.28   $213.30   $213.30  
  Purchase #5 $214.31   8.106%   $231.682   $231.68   $231.70   $231.70  
  Purchase #6 $161.63   8.586%   $175.5076   $175.51   $175.50   $175.50  
  Purchase #7 $184.37   7.661%   $198.4946   $198.49   $198.50   $198.50  
  7 purchase totals = $1,319.68       $1,396.7175   $1,396.71   $1,396.70   $1,396.80