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	$234.89	7.777%	$253.1574	$253.16	$253.15	$253.20
Purchase #2	$168.82	13.602%	$191.7829	$191.78	$191.80	$191.80
Purchase #3	$209.58	3.253%	$216.3976	$216.40	$216.40	$216.40
Purchase #4	$161.42	13.451%	$183.1326	$183.13	$183.15	$183.10
Purchase #5	$19.49	7.135%	$20.8806	$20.88	$20.90	$20.90
Purchase #6	$222.87	5.252%	$234.5751	$234.58	$234.60	$234.60
Purchase #7	$82.37	11.562%	$91.8936	$91.89	$91.90	$91.90
7 purchase totals =	$1,099.44		$1,191.8198	$1,191.82	$1,191.90	$1,191.90