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	$152.83	10.169%	$168.3713	$168.37	$168.35	$168.40
Purchase #2	$100.68	9.551%	$110.2959	$110.30	$110.30	$110.30
Purchase #3	$202.86	3.804%	$210.5768	$210.58	$210.60	$210.60
Purchase #4	$168.48	11.639%	$188.0894	$188.09	$188.10	$188.10
Purchase #5	$122.93	5.307%	$129.4539	$129.45	$129.45	$129.50
Purchase #6	$114.93	7.653%	$123.7256	$123.73	$123.75	$123.70
Purchase #7	$78.45	13.467%	$89.0149	$89.01	$89.00	$89.00
7 purchase totals =	$941.16		$1,019.5278	$1,019.53	$1,019.55	$1,019.60