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	$53.98	6.861%	$57.6836	$57.68	$57.70	$57.70
Purchase #2	$230.27	3.548%	$238.44	$238.44	$238.45	$238.40
Purchase #3	$90.54	9.447%	$99.0933	$99.09	$99.10	$99.10
Purchase #4	$196.40	7.316%	$210.7686	$210.77	$210.75	$210.80
Purchase #5	$16.52	13.467%	$18.7447	$18.74	$18.75	$18.70
Purchase #6	$81.83	9.372%	$89.4991	$89.50	$89.50	$89.50
Purchase #7	$51.33	4.184%	$53.4776	$53.48	$53.50	$53.50
7 purchase totals =	$720.87		$767.7069	$767.70	$767.75	$767.70