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	$166.52	11.545%	$185.7447	$185.74	$185.75	$185.70
Purchase #2	$188.65	10.505%	$208.4677	$208.47	$208.45	$208.50
Purchase #3	$156.58	12.859%	$176.7146	$176.71	$176.70	$176.70
Purchase #4	$26.25	4.625%	$27.4641	$27.46	$27.45	$27.50
Purchase #5	$196.89	5.719%	$208.1501	$208.15	$208.15	$208.20
Purchase #6	$27.66	4.287%	$28.8458	$28.85	$28.85	$28.80
Purchase #7	$79.84	11.759%	$89.2284	$89.23	$89.25	$89.20
7 purchase totals =	$842.39		$924.6154	$924.61	$924.60	$924.60