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	$111.81	3.268%	$115.464	$115.46	$115.45	$115.50
Purchase #2	$238.87	5.375%	$251.7093	$251.71	$251.70	$251.70
Purchase #3	$61.44	7.221%	$65.8766	$65.88	$65.90	$65.90
Purchase #4	$80.78	9.728%	$88.6383	$88.64	$88.65	$88.60
Purchase #5	$38.47	5.644%	$40.6412	$40.64	$40.65	$40.60
Purchase #6	$77.55	3.522%	$80.2813	$80.28	$80.30	$80.30
Purchase #7	$171.57	5.643%	$181.2517	$181.25	$181.25	$181.30
7 purchase totals =	$780.49		$823.8624	$823.86	$823.90	$823.90