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	$17.55	7.784%	$18.9161	$18.92	$18.90	$18.90
Purchase #2	$55.74	12.628%	$62.7788	$62.78	$62.80	$62.80
Purchase #3	$115.29	6.401%	$122.6697	$122.67	$122.65	$122.70
Purchase #4	$40.27	6.229%	$42.7784	$42.78	$42.80	$42.80
Purchase #5	$106.76	8.727%	$116.0769	$116.08	$116.10	$116.10
Purchase #6	$152.39	7.766%	$164.2246	$164.22	$164.20	$164.20
Purchase #7	$174.88	6.192%	$185.7086	$185.71	$185.70	$185.70
7 purchase totals =	$662.88		$713.1531	$713.16	$713.15	$713.20