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	$16.58	4.140%	$17.2664	$17.27	$17.25	$17.30
Purchase #2	$197.88	11.798%	$221.2259	$221.23	$221.25	$221.20
Purchase #3	$18.69	13.755%	$21.2608	$21.26	$21.25	$21.30
Purchase #4	$94.95	6.671%	$101.2841	$101.28	$101.30	$101.30
Purchase #5	$115.27	7.335%	$123.7251	$123.73	$123.75	$123.70
Purchase #6	$95.47	5.220%	$100.4535	$100.45	$100.45	$100.50
Purchase #7	$233.64	6.500%	$248.8266	$248.83	$248.85	$248.80
7 purchase totals =	$772.48		$834.0424	$834.05	$834.10	$834.10