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	$205.60	13.864%	$234.1044	$234.10	$234.10	$234.10
Purchase #2	$242.98	10.841%	$269.3215	$269.32	$269.30	$269.30
Purchase #3	$226.67	12.725%	$255.5138	$255.51	$255.50	$255.50
Purchase #4	$222.96	13.850%	$253.84	$253.84	$253.85	$253.80
Purchase #5	$181.72	3.791%	$188.609	$188.61	$188.60	$188.60
Purchase #6	$244.27	11.836%	$273.1818	$273.18	$273.20	$273.20
Purchase #7	$58.58	6.853%	$62.5945	$62.59	$62.60	$62.60
7 purchase totals =	$1,382.78		$1,537.1650	$1,537.15	$1,537.15	$1,537.10