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	$222.44	3.469%	$230.1564	$230.16	$230.15	$230.20
Purchase #2	$78.60	6.430%	$83.654	$83.65	$83.65	$83.70
Purchase #3	$103.96	11.505%	$115.9206	$115.92	$115.90	$115.90
Purchase #4	$224.59	7.255%	$240.884	$240.88	$240.90	$240.90
Purchase #5	$98.27	4.718%	$102.9064	$102.91	$102.90	$102.90
Purchase #6	$212.30	6.308%	$225.6919	$225.69	$225.70	$225.70
Purchase #7	$49.89	13.171%	$56.461	$56.46	$56.45	$56.50
7 purchase totals =	$990.05		$1,055.6743	$1,055.67	$1,055.65	$1,055.80