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	$107.94	9.415%	$118.1026	$118.10	$118.10	$118.10
Purchase #2	$25.89	10.283%	$28.5523	$28.55	$28.55	$28.60
Purchase #3	$79.39	12.814%	$89.563	$89.56	$89.55	$89.60
Purchase #4	$117.68	5.146%	$123.7358	$123.74	$123.75	$123.70
Purchase #5	$114.89	7.249%	$123.2184	$123.22	$123.20	$123.20
Purchase #6	$64.64	5.311%	$68.073	$68.07	$68.05	$68.10
Purchase #7	$89.47	12.401%	$100.5652	$100.57	$100.55	$100.60
7 purchase totals =	$599.90		$651.8103	$651.81	$651.75	$651.90