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	$111.47	6.199%	$118.38	$118.38	$118.40	$118.40
Purchase #2	$79.49	12.530%	$89.4501	$89.45	$89.45	$89.50
Purchase #3	$41.39	3.789%	$42.9583	$42.96	$42.95	$43.00
Purchase #4	$200.61	9.793%	$220.2557	$220.26	$220.25	$220.30
Purchase #5	$97.37	10.179%	$107.2813	$107.28	$107.30	$107.30
Purchase #6	$134.40	10.149%	$148.0403	$148.04	$148.05	$148.00
Purchase #7	$74.55	12.223%	$83.6622	$83.66	$83.65	$83.70
7 purchase totals =	$739.28		$810.0279	$810.03	$810.05	$810.20