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	$19.50	4.603%	$20.3976	$20.40	$20.40	$20.40
Purchase #2	$200.49	11.405%	$223.3559	$223.36	$223.35	$223.40
Purchase #3	$81.85	13.249%	$92.6943	$92.69	$92.70	$92.70
Purchase #4	$47.36	12.799%	$53.4216	$53.42	$53.40	$53.40
Purchase #5	$119.59	12.275%	$134.2697	$134.27	$134.25	$134.30
Purchase #6	$88.41	13.286%	$100.1562	$100.16	$100.15	$100.20
Purchase #7	$175.54	5.627%	$185.4176	$185.42	$185.40	$185.40
7 purchase totals =	$732.74		$809.7129	$809.72	$809.65	$809.80