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	$42.90	8.795%	$46.6731	$46.67	$46.65	$46.70
Purchase #2	$91.98	8.130%	$99.458	$99.46	$99.45	$99.50
Purchase #3	$53.53	4.543%	$55.9619	$55.96	$55.95	$56.00
Purchase #4	$19.45	11.858%	$21.7564	$21.76	$21.75	$21.80
Purchase #5	$101.32	12.566%	$114.0519	$114.05	$114.05	$114.10
Purchase #6	$17.79	4.586%	$18.6058	$18.61	$18.60	$18.60
Purchase #7	$179.85	10.477%	$198.6929	$198.69	$198.70	$198.70
7 purchase totals =	$506.82		$555.2000	$555.20	$555.15	$555.40