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	$56.37	13.517%	$63.9895	$63.99	$64.00	$64.00
Purchase #2	$111.92	6.396%	$119.0784	$119.08	$119.10	$119.10
Purchase #3	$99.88	4.244%	$104.1189	$104.12	$104.10	$104.10
Purchase #4	$39.71	6.702%	$42.3714	$42.37	$42.35	$42.40
Purchase #5	$233.49	7.736%	$251.5528	$251.55	$251.55	$251.60
Purchase #6	$250.56	11.743%	$279.9833	$279.98	$280.00	$280.00
Purchase #7	$220.78	6.222%	$234.5169	$234.52	$234.50	$234.50
7 purchase totals =	$1,012.71		$1,095.6112	$1,095.61	$1,095.60	$1,095.70