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	$47.87	6.181%	$50.8288	$50.83	$50.85	$50.80
Purchase #2	$247.83	3.276%	$255.9489	$255.95	$255.95	$255.90
Purchase #3	$180.32	5.741%	$190.6722	$190.67	$190.65	$190.70
Purchase #4	$246.85	5.664%	$260.8316	$260.83	$260.85	$260.80
Purchase #5	$194.91	9.196%	$212.8339	$212.83	$212.85	$212.80
Purchase #6	$89.72	7.679%	$96.6096	$96.61	$96.60	$96.60
Purchase #7	$28.95	6.739%	$30.9009	$30.90	$30.90	$30.90
7 purchase totals =	$1,036.45		$1,098.6259	$1,098.62	$1,098.65	$1,098.50