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	$142.37	13.302%	$161.3081	$161.31	$161.30	$161.30
Purchase #2	$240.47	12.123%	$269.6222	$269.62	$269.60	$269.60
Purchase #3	$60.40	6.838%	$64.5302	$64.53	$64.55	$64.50
Purchase #4	$250.62	9.769%	$275.1031	$275.10	$275.10	$275.10
Purchase #5	$207.66	10.867%	$230.2264	$230.23	$230.25	$230.20
Purchase #6	$82.55	8.545%	$89.6039	$89.60	$89.60	$89.60
Purchase #7	$142.96	12.155%	$160.3368	$160.34	$160.35	$160.30
7 purchase totals =	$1,127.03		$1,250.7307	$1,250.73	$1,250.75	$1,250.60