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	$140.37	8.663%	$152.5303	$152.53	$152.55	$152.50
Purchase #2	$93.95	6.497%	$100.0539	$100.05	$100.05	$100.10
Purchase #3	$20.57	8.739%	$22.3676	$22.37	$22.35	$22.40
Purchase #4	$12.71	12.184%	$14.2586	$14.26	$14.25	$14.30
Purchase #5	$117.77	4.670%	$123.2699	$123.27	$123.25	$123.30
Purchase #6	$40.90	5.517%	$43.1565	$43.16	$43.15	$43.20
Purchase #7	$142.59	3.866%	$148.1025	$148.10	$148.10	$148.10
7 purchase totals =	$568.86		$603.7393	$603.74	$603.70	$603.90