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	$35.35	12.285%	$39.6927	$39.69	$39.70	$39.70
Purchase #2	$75.95	4.557%	$79.411	$79.41	$79.40	$79.40
Purchase #3	$216.52	13.238%	$245.1829	$245.18	$245.20	$245.20
Purchase #4	$103.42	7.568%	$111.2468	$111.25	$111.25	$111.20
Purchase #5	$198.70	12.310%	$223.16	$223.16	$223.15	$223.20
Purchase #6	$216.99	11.728%	$242.4386	$242.44	$242.45	$242.40
Purchase #7	$214.49	4.379%	$223.8825	$223.88	$223.90	$223.90
7 purchase totals =	$1,061.42		$1,165.0145	$1,165.01	$1,165.05	$1,165.00