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	$23.89	8.226%	$25.8552	$25.86	$25.85	$25.90
Purchase #2	$244.90	8.802%	$266.4561	$266.46	$266.45	$266.50
Purchase #3	$42.39	3.175%	$43.7359	$43.74	$43.75	$43.70
Purchase #4	$166.72	11.460%	$185.8261	$185.83	$185.85	$185.80
Purchase #5	$185.82	8.250%	$201.1502	$201.15	$201.15	$201.20
Purchase #6	$5.89	5.828%	$6.2333	$6.23	$6.25	$6.20
Purchase #7	$32.71	13.203%	$37.0287	$37.03	$37.05	$37.00
7 purchase totals =	$702.32		$766.2855	$766.30	$766.35	$766.30