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	$121.30	13.379%	$137.5287	$137.53	$137.55	$137.50
Purchase #2	$206.93	6.280%	$219.9252	$219.93	$219.95	$219.90
Purchase #3	$71.83	10.169%	$79.1344	$79.13	$79.15	$79.10
Purchase #4	$56.26	10.771%	$62.3198	$62.32	$62.30	$62.30
Purchase #5	$236.91	6.337%	$251.923	$251.92	$251.90	$251.90
Purchase #6	$100.60	8.376%	$109.0263	$109.03	$109.05	$109.00
Purchase #7	$147.31	7.569%	$158.4599	$158.46	$158.45	$158.50
7 purchase totals =	$941.14		$1,018.3173	$1,018.32	$1,018.35	$1,018.20