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	$43.63	10.477%	$48.2011	$48.20	$48.20	$48.20
Purchase #2	$79.41	8.481%	$86.1448	$86.14	$86.15	$86.10
Purchase #3	$83.68	9.175%	$91.3576	$91.36	$91.35	$91.40
Purchase #4	$103.84	7.503%	$111.6311	$111.63	$111.65	$111.60
Purchase #5	$123.61	13.600%	$140.421	$140.42	$140.40	$140.40
Purchase #6	$11.60	5.403%	$12.2267	$12.23	$12.25	$12.20
Purchase #7	$29.54	11.343%	$32.8907	$32.89	$32.90	$32.90
7 purchase totals =	$475.31		$522.8730	$522.87	$522.90	$522.80