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	$6.58	8.120%	$7.1143	$7.11	$7.10	$7.10
Purchase #2	$53.47	9.223%	$58.4015	$58.40	$58.40	$58.40
Purchase #3	$55.89	13.820%	$63.614	$63.61	$63.60	$63.60
Purchase #4	$193.77	11.176%	$215.4257	$215.43	$215.45	$215.40
Purchase #5	$35.72	8.119%	$38.6201	$38.62	$38.60	$38.60
Purchase #6	$50.41	10.315%	$55.6098	$55.61	$55.60	$55.60
Purchase #7	$58.59	12.335%	$65.8171	$65.82	$65.80	$65.80
7 purchase totals =	$454.43		$504.6025	$504.60	$504.55	$504.50