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	$81.91	7.606%	$88.1401	$88.14	$88.15	$88.10
Purchase #2	$157.84	4.183%	$164.4424	$164.44	$164.45	$164.40
Purchase #3	$233.56	9.524%	$255.8043	$255.80	$255.80	$255.80
Purchase #4	$35.43	12.681%	$39.9229	$39.92	$39.90	$39.90
Purchase #5	$185.57	4.720%	$194.3289	$194.33	$194.35	$194.30
Purchase #6	$152.28	13.328%	$172.5759	$172.58	$172.60	$172.60
Purchase #7	$145.52	8.847%	$158.3942	$158.39	$158.40	$158.40
7 purchase totals =	$992.11		$1,073.6087	$1,073.60	$1,073.65	$1,073.50