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	$22.55	13.472%	$25.5879	$25.59	$25.60	$25.60
Purchase #2	$40.57	4.232%	$42.2869	$42.29	$42.30	$42.30
Purchase #3	$72.46	9.383%	$79.2589	$79.26	$79.25	$79.30
Purchase #4	$84.56	3.236%	$87.2964	$87.30	$87.30	$87.30
Purchase #5	$200.30	5.152%	$210.6195	$210.62	$210.60	$210.60
Purchase #6	$116.92	8.867%	$127.2873	$127.29	$127.30	$127.30
Purchase #7	$105.97	9.375%	$115.9047	$115.90	$115.90	$115.90
7 purchase totals =	$643.33		$688.2416	$688.25	$688.25	$688.30