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	$141.72	9.316%	$154.9226	$154.92	$154.90	$154.90
Purchase #2	$208.55	13.796%	$237.3216	$237.32	$237.30	$237.30
Purchase #3	$123.54	8.722%	$134.3152	$134.32	$134.30	$134.30
Purchase #4	$111.96	7.109%	$119.9192	$119.92	$119.90	$119.90
Purchase #5	$245.65	13.633%	$279.1395	$279.14	$279.15	$279.10
Purchase #6	$121.66	4.755%	$127.4449	$127.44	$127.45	$127.40
Purchase #7	$33.93	3.821%	$35.2265	$35.23	$35.25	$35.20
7 purchase totals =	$987.01		$1,088.2895	$1,088.29	$1,088.25	$1,088.10