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	$20.53	13.839%	$23.3711	$23.37	$23.35	$23.40
Purchase #2	$70.88	7.470%	$76.1747	$76.17	$76.15	$76.20
Purchase #3	$85.81	4.771%	$89.904	$89.90	$89.90	$89.90
Purchase #4	$69.27	3.658%	$71.8039	$71.80	$71.80	$71.80
Purchase #5	$19.57	6.756%	$20.8921	$20.89	$20.90	$20.90
Purchase #6	$158.91	9.285%	$173.6648	$173.66	$173.65	$173.70
Purchase #7	$245.46	13.804%	$279.3433	$279.34	$279.35	$279.30
7 purchase totals =	$670.43		$735.1539	$735.13	$735.10	$735.20