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	$138.52	9.255%	$151.34	$151.34	$151.35	$151.30
Purchase #2	$72.81	7.231%	$78.0749	$78.07	$78.05	$78.10
Purchase #3	$226.69	8.303%	$245.5121	$245.51	$245.50	$245.50
Purchase #4	$73.63	13.705%	$83.721	$83.72	$83.70	$83.70
Purchase #5	$63.33	12.382%	$71.1715	$71.17	$71.15	$71.20
Purchase #6	$51.87	5.725%	$54.8396	$54.84	$54.85	$54.80
Purchase #7	$142.25	7.618%	$153.0866	$153.09	$153.10	$153.10
7 purchase totals =	$769.10		$837.7457	$837.74	$837.70	$837.70