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	$220.67	6.427%	$234.8525	$234.85	$234.85	$234.90
Purchase #2	$89.84	11.497%	$100.1689	$100.17	$100.15	$100.20
Purchase #3	$32.67	7.535%	$35.1317	$35.13	$35.15	$35.10
Purchase #4	$168.58	4.484%	$176.1391	$176.14	$176.15	$176.10
Purchase #5	$116.61	8.281%	$126.2665	$126.27	$126.25	$126.30
Purchase #6	$79.51	13.335%	$90.1127	$90.11	$90.10	$90.10
Purchase #7	$19.57	4.376%	$20.4264	$20.43	$20.45	$20.40
7 purchase totals =	$727.45		$783.0978	$783.10	$783.10	$783.10