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	$15.69	13.406%	$17.7934	$17.79	$17.80	$17.80
Purchase #2	$243.52	9.592%	$266.8784	$266.88	$266.90	$266.90
Purchase #3	$92.97	6.786%	$99.2789	$99.28	$99.30	$99.30
Purchase #4	$155.27	12.534%	$174.7315	$174.73	$174.75	$174.70
Purchase #5	$218.79	6.717%	$233.4861	$233.49	$233.50	$233.50
Purchase #6	$112.75	7.250%	$120.9244	$120.92	$120.90	$120.90
Purchase #7	$100.89	5.736%	$106.6771	$106.68	$106.70	$106.70
7 purchase totals =	$939.88		$1,019.7698	$1,019.77	$1,019.85	$1,019.80