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	$20.55	7.181%	$22.0257	$22.03	$22.05	$22.00
Purchase #2	$159.28	13.485%	$180.7589	$180.76	$180.75	$180.80
Purchase #3	$19.72	6.834%	$21.0677	$21.07	$21.05	$21.10
Purchase #4	$64.65	11.612%	$72.1572	$72.16	$72.15	$72.20
Purchase #5	$201.42	13.837%	$229.2905	$229.29	$229.30	$229.30
Purchase #6	$142.86	13.433%	$162.0504	$162.05	$162.05	$162.10
Purchase #7	$51.71	4.499%	$54.0364	$54.04	$54.05	$54.00
7 purchase totals =	$660.19		$741.3868	$741.40	$741.40	$741.50