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	$73.31	7.681%	$78.9409	$78.94	$78.95	$78.90
Purchase #2	$107.85	5.348%	$113.6178	$113.62	$113.60	$113.60
Purchase #3	$171.54	3.351%	$177.2883	$177.29	$177.30	$177.30
Purchase #4	$40.93	12.288%	$45.9595	$45.96	$45.95	$46.00
Purchase #5	$126.60	8.468%	$137.3205	$137.32	$137.30	$137.30
Purchase #6	$160.33	3.121%	$165.3339	$165.33	$165.35	$165.30
Purchase #7	$226.54	10.521%	$250.3743	$250.37	$250.35	$250.40
7 purchase totals =	$907.10		$968.8352	$968.83	$968.80	$968.80