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	$17.68	5.258%	$18.6096	$18.61	$18.60	$18.60
Purchase #2	$99.60	11.623%	$111.1765	$111.18	$111.20	$111.20
Purchase #3	$155.43	10.374%	$171.5543	$171.55	$171.55	$171.60
Purchase #4	$60.53	13.814%	$68.8916	$68.89	$68.90	$68.90
Purchase #5	$139.60	4.384%	$145.7201	$145.72	$145.70	$145.70
Purchase #6	$51.36	3.156%	$52.9809	$52.98	$53.00	$53.00
Purchase #7	$93.66	5.532%	$98.8413	$98.84	$98.85	$98.80
7 purchase totals =	$617.86		$667.7743	$667.77	$667.80	$667.80