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	$165.44	13.304%	$187.4501	$187.45	$187.45	$187.50
Purchase #2	$130.28	11.144%	$144.7984	$144.80	$144.80	$144.80
Purchase #3	$109.72	5.508%	$115.7634	$115.76	$115.75	$115.80
Purchase #4	$152.64	13.454%	$173.1762	$173.18	$173.20	$173.20
Purchase #5	$70.39	12.103%	$78.9093	$78.91	$78.90	$78.90
Purchase #6	$174.59	4.756%	$182.8935	$182.89	$182.90	$182.90
Purchase #7	$109.84	4.230%	$114.4862	$114.49	$114.50	$114.50
7 purchase totals =	$912.90		$997.4771	$997.48	$997.50	$997.60