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	$212.43	12.356%	$238.6779	$238.68	$238.70	$238.70
Purchase #2	$63.50	8.604%	$68.9635	$68.96	$68.95	$69.00
Purchase #3	$211.56	6.171%	$224.6154	$224.62	$224.60	$224.60
Purchase #4	$145.63	13.861%	$165.8158	$165.82	$165.80	$165.80
Purchase #5	$93.92	11.342%	$104.5724	$104.57	$104.55	$104.60
Purchase #6	$39.79	6.700%	$42.4559	$42.46	$42.45	$42.50
Purchase #7	$76.79	8.453%	$83.2811	$83.28	$83.30	$83.30
7 purchase totals =	$843.62		$928.3820	$928.39	$928.35	$928.50