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	$109.38	8.288%	$118.4454	$118.45	$118.45	$118.40
Purchase #2	$237.77	4.406%	$248.2461	$248.25	$248.25	$248.20
Purchase #3	$18.59	12.521%	$20.9177	$20.92	$20.90	$20.90
Purchase #4	$48.68	10.447%	$53.7656	$53.77	$53.75	$53.80
Purchase #5	$61.57	4.671%	$64.4459	$64.45	$64.45	$64.40
Purchase #6	$35.75	12.800%	$40.326	$40.33	$40.35	$40.30
Purchase #7	$108.77	11.562%	$121.346	$121.35	$121.35	$121.30
7 purchase totals =	$620.51		$667.4927	$667.52	$667.50	$667.30