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	$91.91	8.704%	$99.9098	$99.91	$99.90	$99.90
Purchase #2	$37.88	6.642%	$40.396	$40.40	$40.40	$40.40
Purchase #3	$174.37	10.191%	$192.14	$192.14	$192.15	$192.10
Purchase #4	$62.77	6.809%	$67.044	$67.04	$67.05	$67.00
Purchase #5	$127.43	13.462%	$144.5846	$144.58	$144.60	$144.60
Purchase #6	$81.55	7.378%	$87.5668	$87.57	$87.55	$87.60
Purchase #7	$19.77	8.614%	$21.473	$21.47	$21.45	$21.50
7 purchase totals =	$595.68		$653.1142	$653.11	$653.10	$653.10