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	$54.38	3.797%	$56.4448	$56.44	$56.45	$56.40
Purchase #2	$104.93	3.770%	$108.8859	$108.89	$108.90	$108.90
Purchase #3	$73.92	4.573%	$77.3004	$77.30	$77.30	$77.30
Purchase #4	$57.79	9.259%	$63.1408	$63.14	$63.15	$63.10
Purchase #5	$84.82	5.182%	$89.2154	$89.22	$89.20	$89.20
Purchase #6	$119.43	3.824%	$123.997	$124.00	$124.00	$124.00
Purchase #7	$134.73	11.707%	$150.5028	$150.50	$150.50	$150.50
7 purchase totals =	$630.00		$669.4871	$669.49	$669.50	$669.40