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	$175.34	5.648%	$185.2432	$185.24	$185.25	$185.20
Purchase #2	$109.93	12.179%	$123.3184	$123.32	$123.30	$123.30
Purchase #3	$111.82	10.429%	$123.4817	$123.48	$123.50	$123.50
Purchase #4	$100.52	8.842%	$109.408	$109.41	$109.40	$109.40
Purchase #5	$123.87	5.574%	$130.7745	$130.77	$130.75	$130.80
Purchase #6	$90.39	12.626%	$101.8026	$101.80	$101.80	$101.80
Purchase #7	$19.70	12.777%	$22.2171	$22.22	$22.20	$22.20
7 purchase totals =	$731.57		$796.2455	$796.24	$796.20	$796.20