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	$40.57	4.540%	$42.4119	$42.41	$42.40	$42.40
Purchase #2	$139.25	5.176%	$146.4576	$146.46	$146.45	$146.50
Purchase #3	$22.29	13.724%	$25.3491	$25.35	$25.35	$25.30
Purchase #4	$73.27	7.378%	$78.6759	$78.68	$78.70	$78.70
Purchase #5	$217.56	9.697%	$238.6568	$238.66	$238.65	$238.70
Purchase #6	$111.58	8.616%	$121.1937	$121.19	$121.20	$121.20
Purchase #7	$121.80	5.550%	$128.5599	$128.56	$128.55	$128.60
7 purchase totals =	$726.32		$781.3049	$781.31	$781.30	$781.40