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	$216.74	6.823%	$231.5282	$231.53	$231.55	$231.50
Purchase #2	$81.73	9.468%	$89.4682	$89.47	$89.45	$89.50
Purchase #3	$72.39	4.715%	$75.8032	$75.80	$75.80	$75.80
Purchase #4	$74.96	10.478%	$82.8143	$82.81	$82.80	$82.80
Purchase #5	$10.93	13.838%	$12.4425	$12.44	$12.45	$12.40
Purchase #6	$205.49	13.783%	$233.8127	$233.81	$233.80	$233.80
Purchase #7	$104.70	4.686%	$109.6062	$109.61	$109.60	$109.60
7 purchase totals =	$766.94		$835.4753	$835.47	$835.45	$835.40