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	$105.70	5.506%	$111.5198	$111.52	$111.50	$111.50
Purchase #2	$197.85	4.282%	$206.3219	$206.32	$206.30	$206.30
Purchase #3	$35.85	11.551%	$39.991	$39.99	$40.00	$40.00
Purchase #4	$196.82	3.868%	$204.433	$204.43	$204.45	$204.40
Purchase #5	$172.56	4.392%	$180.1388	$180.14	$180.15	$180.10
Purchase #6	$91.81	7.174%	$98.3964	$98.40	$98.40	$98.40
Purchase #7	$124.55	10.324%	$137.4085	$137.41	$137.40	$137.40
7 purchase totals =	$925.14		$978.2094	$978.21	$978.20	$978.10