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	$79.71	13.647%	$90.588	$90.59	$90.60	$90.60
Purchase #2	$203.84	8.561%	$221.2907	$221.29	$221.30	$221.30
Purchase #3	$235.80	8.825%	$256.6094	$256.61	$256.60	$256.60
Purchase #4	$219.73	3.578%	$227.5919	$227.59	$227.60	$227.60
Purchase #5	$87.46	4.313%	$91.2321	$91.23	$91.25	$91.20
Purchase #6	$188.39	10.300%	$207.7942	$207.79	$207.80	$207.80
Purchase #7	$174.77	7.238%	$187.4199	$187.42	$187.40	$187.40
7 purchase totals =	$1,189.70		$1,282.5262	$1,282.52	$1,282.55	$1,282.50