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	$91.44	9.341%	$99.9814	$99.98	$100.00	$100.00
Purchase #2	$172.81	8.146%	$186.8871	$186.89	$186.90	$186.90
Purchase #3	$12.52	7.361%	$13.4416	$13.44	$13.45	$13.40
Purchase #4	$71.38	11.731%	$79.7536	$79.75	$79.75	$79.80
Purchase #5	$12.70	5.778%	$13.4338	$13.43	$13.45	$13.40
Purchase #6	$65.55	11.541%	$73.1151	$73.12	$73.10	$73.10
Purchase #7	$20.99	4.253%	$21.8827	$21.88	$21.90	$21.90
7 purchase totals =	$447.39		$488.4953	$488.49	$488.55	$488.50