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	$112.29	8.313%	$121.6247	$121.62	$121.60	$121.60
Purchase #2	$127.58	10.696%	$141.226	$141.23	$141.25	$141.20
Purchase #3	$124.83	9.160%	$136.2644	$136.26	$136.25	$136.30
Purchase #4	$223.30	6.850%	$238.5961	$238.60	$238.60	$238.60
Purchase #5	$53.85	3.606%	$55.7918	$55.79	$55.80	$55.80
Purchase #6	$112.51	13.307%	$127.4817	$127.48	$127.50	$127.50
Purchase #7	$196.98	11.502%	$219.6366	$219.64	$219.65	$219.60
7 purchase totals =	$951.34		$1,040.6213	$1,040.62	$1,040.65	$1,040.60