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	$34.90	6.607%	$37.2058	$37.21	$37.20	$37.20
Purchase #2	$156.59	13.766%	$178.1462	$178.15	$178.15	$178.10
Purchase #3	$111.81	3.253%	$115.4472	$115.45	$115.45	$115.40
Purchase #4	$92.80	7.215%	$99.4955	$99.50	$99.50	$99.50
Purchase #5	$215.74	9.337%	$235.8836	$235.88	$235.90	$235.90
Purchase #6	$25.98	9.673%	$28.493	$28.49	$28.50	$28.50
Purchase #7	$194.61	5.132%	$204.5974	$204.60	$204.60	$204.60
7 purchase totals =	$832.43		$899.2687	$899.28	$899.30	$899.20