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	$12.61	3.156%	$13.008	$13.01	$13.00	$13.00
Purchase #2	$184.73	3.628%	$191.432	$191.43	$191.45	$191.40
Purchase #3	$124.93	13.725%	$142.0766	$142.08	$142.10	$142.10
Purchase #4	$7.43	3.796%	$7.712	$7.71	$7.70	$7.70
Purchase #5	$102.93	4.114%	$107.1645	$107.16	$107.15	$107.20
Purchase #6	$113.26	9.485%	$124.0027	$124.00	$124.00	$124.00
Purchase #7	$73.42	12.246%	$82.411	$82.41	$82.40	$82.40
7 purchase totals =	$619.31		$667.8068	$667.80	$667.80	$667.80