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	$172.88	3.577%	$179.0639	$179.06	$179.05	$179.10
Purchase #2	$19.36	3.791%	$20.0939	$20.09	$20.10	$20.10
Purchase #3	$156.35	5.713%	$165.2823	$165.28	$165.30	$165.30
Purchase #4	$171.75	8.218%	$185.8644	$185.86	$185.85	$185.90
Purchase #5	$34.37	10.364%	$37.9321	$37.93	$37.95	$37.90
Purchase #6	$185.36	12.386%	$208.3187	$208.32	$208.30	$208.30
Purchase #7	$18.28	3.553%	$18.9295	$18.93	$18.95	$18.90
7 purchase totals =	$758.35		$815.4848	$815.47	$815.50	$815.50