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	$134.39	3.256%	$138.7657	$138.77	$138.75	$138.80
Purchase #2	$199.83	5.303%	$210.427	$210.43	$210.45	$210.40
Purchase #3	$234.39	8.194%	$253.5959	$253.60	$253.60	$253.60
Purchase #4	$202.29	10.518%	$223.5669	$223.57	$223.55	$223.60
Purchase #5	$174.69	12.371%	$196.3009	$196.30	$196.30	$196.30
Purchase #6	$114.78	7.771%	$123.6996	$123.70	$123.70	$123.70
Purchase #7	$80.94	9.719%	$88.8066	$88.81	$88.80	$88.80
7 purchase totals =	$1,141.31		$1,235.1626	$1,235.18	$1,235.15	$1,235.20