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	$233.35	6.473%	$248.4547	$248.45	$248.45	$248.50
Purchase #2	$90.59	8.843%	$98.6009	$98.60	$98.60	$98.60
Purchase #3	$58.58	5.213%	$61.6338	$61.63	$61.65	$61.60
Purchase #4	$58.98	10.377%	$65.1004	$65.10	$65.10	$65.10
Purchase #5	$81.92	10.328%	$90.3807	$90.38	$90.40	$90.40
Purchase #6	$200.74	10.416%	$221.6491	$221.65	$221.65	$221.60
Purchase #7	$56.30	6.859%	$60.1616	$60.16	$60.15	$60.20
7 purchase totals =	$780.46		$845.9812	$845.97	$846.00	$846.00