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	$17.53	3.782%	$18.193	$18.19	$18.20	$18.20
Purchase #2	$219.60	10.604%	$242.8864	$242.89	$242.90	$242.90
Purchase #3	$164.40	12.542%	$185.019	$185.02	$185.00	$185.00
Purchase #4	$12.31	11.721%	$13.7529	$13.75	$13.75	$13.80
Purchase #5	$243.87	10.209%	$268.7667	$268.77	$268.75	$268.80
Purchase #6	$123.36	11.296%	$137.2947	$137.29	$137.30	$137.30
Purchase #7	$217.71	7.176%	$233.3329	$233.33	$233.35	$233.30
7 purchase totals =	$998.78		$1,099.2456	$1,099.24	$1,099.25	$1,099.30