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	$54.29	3.550%	$56.2173	$56.22	$56.20	$56.20
Purchase #2	$134.48	3.855%	$139.6642	$139.66	$139.65	$139.70
Purchase #3	$85.77	10.175%	$94.4971	$94.50	$94.50	$94.50
Purchase #4	$166.35	3.632%	$172.3918	$172.39	$172.40	$172.40
Purchase #5	$29.70	8.400%	$32.1948	$32.19	$32.20	$32.20
Purchase #6	$152.52	10.676%	$168.803	$168.80	$168.80	$168.80
Purchase #7	$160.40	7.712%	$172.77	$172.77	$172.75	$172.80
7 purchase totals =	$783.51		$836.5382	$836.53	$836.50	$836.60