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	$91.45	9.267%	$99.9247	$99.92	$99.90	$99.90
Purchase #2	$18.95	8.599%	$20.5795	$20.58	$20.60	$20.60
Purchase #3	$161.54	8.139%	$174.6877	$174.69	$174.70	$174.70
Purchase #4	$250.71	5.615%	$264.7874	$264.79	$264.80	$264.80
Purchase #5	$22.30	11.420%	$24.8467	$24.85	$24.85	$24.80
Purchase #6	$205.83	5.233%	$216.6011	$216.60	$216.60	$216.60
Purchase #7	$100.60	8.231%	$108.8804	$108.88	$108.90	$108.90
7 purchase totals =	$851.38		$910.3075	$910.31	$910.35	$910.30