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	$57.91	12.789%	$65.3161	$65.32	$65.30	$65.30
Purchase #2	$101.51	5.743%	$107.3397	$107.34	$107.35	$107.30
Purchase #3	$111.72	13.193%	$126.4592	$126.46	$126.45	$126.50
Purchase #4	$233.98	6.339%	$248.812	$248.81	$248.80	$248.80
Purchase #5	$225.61	10.551%	$249.4141	$249.41	$249.40	$249.40
Purchase #6	$149.35	12.765%	$168.4145	$168.41	$168.40	$168.40
Purchase #7	$118.31	10.585%	$130.8331	$130.83	$130.85	$130.80
7 purchase totals =	$998.39		$1,096.5887	$1,096.58	$1,096.55	$1,096.50