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	$173.83	12.355%	$195.3067	$195.31	$195.30	$195.30
Purchase #2	$92.83	8.252%	$100.4903	$100.49	$100.50	$100.50
Purchase #3	$214.84	7.687%	$231.3548	$231.35	$231.35	$231.40
Purchase #4	$82.97	9.254%	$90.648	$90.65	$90.65	$90.60
Purchase #5	$142.54	6.623%	$151.9804	$151.98	$152.00	$152.00
Purchase #6	$102.25	5.527%	$107.9014	$107.90	$107.90	$107.90
Purchase #7	$130.38	9.492%	$142.7557	$142.76	$142.75	$142.80
7 purchase totals =	$939.64		$1,020.4373	$1,020.44	$1,020.45	$1,020.50