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	$111.41	5.804%	$117.8762	$117.88	$117.90	$117.90
Purchase #2	$34.45	13.617%	$39.1411	$39.14	$39.15	$39.10
Purchase #3	$67.29	6.537%	$71.6887	$71.69	$71.70	$71.70
Purchase #4	$98.54	13.550%	$111.8922	$111.89	$111.90	$111.90
Purchase #5	$170.76	8.852%	$185.8757	$185.88	$185.90	$185.90
Purchase #6	$42.73	4.813%	$44.7866	$44.79	$44.80	$44.80
Purchase #7	$108.40	12.825%	$122.3023	$122.30	$122.30	$122.30
7 purchase totals =	$633.58		$693.5628	$693.57	$693.65	$693.60