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	$61.61	12.498%	$69.31	$69.31	$69.30	$69.30
Purchase #2	$84.31	6.244%	$89.5743	$89.57	$89.55	$89.60
Purchase #3	$12.66	8.699%	$13.7613	$13.76	$13.75	$13.80
Purchase #4	$201.82	3.867%	$209.6244	$209.62	$209.60	$209.60
Purchase #5	$35.65	9.779%	$39.1362	$39.14	$39.15	$39.10
Purchase #6	$128.65	8.501%	$139.5865	$139.59	$139.60	$139.60
Purchase #7	$248.56	13.773%	$282.7942	$282.79	$282.80	$282.80
7 purchase totals =	$773.26		$843.7869	$843.78	$843.75	$843.80