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	$152.43	4.294%	$158.9753	$158.98	$159.00	$159.00
Purchase #2	$53.59	7.178%	$57.4367	$57.44	$57.45	$57.40
Purchase #3	$16.40	11.431%	$18.2747	$18.27	$18.25	$18.30
Purchase #4	$59.37	4.617%	$62.1111	$62.11	$62.10	$62.10
Purchase #5	$50.46	3.856%	$52.4057	$52.41	$52.40	$52.40
Purchase #6	$170.25	8.865%	$185.3427	$185.34	$185.35	$185.30
Purchase #7	$50.31	12.154%	$56.4247	$56.42	$56.40	$56.40
7 purchase totals =	$552.81		$590.9709	$590.97	$590.95	$590.90