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	$139.30	6.604%	$148.4994	$148.50	$148.50	$148.50
Purchase #2	$67.90	8.147%	$73.4318	$73.43	$73.45	$73.40
Purchase #3	$97.42	9.491%	$106.6661	$106.67	$106.65	$106.70
Purchase #4	$53.72	10.627%	$59.4288	$59.43	$59.45	$59.40
Purchase #5	$173.65	10.303%	$191.5412	$191.54	$191.55	$191.50
Purchase #6	$188.54	8.772%	$205.0787	$205.08	$205.10	$205.10
Purchase #7	$191.58	13.859%	$218.1311	$218.13	$218.15	$218.10
7 purchase totals =	$912.11		$1,002.7771	$1,002.78	$1,002.85	$1,002.70