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	$78.74	4.695%	$82.4368	$82.44	$82.45	$82.40
Purchase #2	$206.81	13.487%	$234.7025	$234.70	$234.70	$234.70
Purchase #3	$91.65	13.685%	$104.1923	$104.19	$104.20	$104.20
Purchase #4	$148.52	6.705%	$158.4783	$158.48	$158.50	$158.50
Purchase #5	$166.34	3.448%	$172.0754	$172.08	$172.10	$172.10
Purchase #6	$43.85	6.403%	$46.6577	$46.66	$46.65	$46.70
Purchase #7	$52.87	13.234%	$59.8668	$59.87	$59.85	$59.90
7 purchase totals =	$788.78		$858.4098	$858.42	$858.45	$858.50