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	$108.33	7.828%	$116.8101	$116.81	$116.80	$116.80
Purchase #2	$235.68	8.632%	$256.0239	$256.02	$256.00	$256.00
Purchase #3	$165.30	13.606%	$187.7907	$187.79	$187.80	$187.80
Purchase #4	$230.59	3.346%	$238.3055	$238.31	$238.30	$238.30
Purchase #5	$249.86	5.428%	$263.4224	$263.42	$263.40	$263.40
Purchase #6	$169.90	6.197%	$180.4287	$180.43	$180.45	$180.40
Purchase #7	$53.25	8.453%	$57.7512	$57.75	$57.75	$57.80
7 purchase totals =	$1,212.91		$1,300.5325	$1,300.53	$1,300.50	$1,300.50