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	$151.37	8.674%	$164.4998	$164.50	$164.50	$164.50
Purchase #2	$141.72	11.761%	$158.3877	$158.39	$158.40	$158.40
Purchase #3	$103.71	13.785%	$118.0064	$118.01	$118.00	$118.00
Purchase #4	$31.46	6.566%	$33.5257	$33.53	$33.55	$33.50
Purchase #5	$42.54	12.142%	$47.7052	$47.71	$47.70	$47.70
Purchase #6	$207.57	10.717%	$229.8153	$229.82	$229.80	$229.80
Purchase #7	$74.58	5.251%	$78.4962	$78.50	$78.50	$78.50
7 purchase totals =	$752.95		$830.4363	$830.46	$830.45	$830.40