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	$70.32	11.817%	$78.6297	$78.63	$78.65	$78.60
Purchase #2	$110.84	13.215%	$125.4875	$125.49	$125.50	$125.50
Purchase #3	$32.34	9.601%	$35.445	$35.45	$35.45	$35.40
Purchase #4	$91.82	12.829%	$103.5996	$103.60	$103.60	$103.60
Purchase #5	$38.77	11.135%	$43.087	$43.09	$43.10	$43.10
Purchase #6	$87.49	3.471%	$90.5268	$90.53	$90.55	$90.50
Purchase #7	$183.95	4.714%	$192.6214	$192.62	$192.60	$192.60
7 purchase totals =	$615.53		$669.3970	$669.41	$669.45	$669.30