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	$121.65	12.329%	$136.6482	$136.65	$136.65	$136.60
Purchase #2	$156.96	3.212%	$162.0016	$162.00	$162.00	$162.00
Purchase #3	$123.33	3.676%	$127.8636	$127.86	$127.85	$127.90
Purchase #4	$228.52	12.390%	$256.8336	$256.83	$256.85	$256.80
Purchase #5	$144.90	10.758%	$160.4883	$160.49	$160.50	$160.50
Purchase #6	$139.42	6.758%	$148.842	$148.84	$148.85	$148.80
Purchase #7	$23.56	11.492%	$26.2675	$26.27	$26.25	$26.30
7 purchase totals =	$938.34		$1,018.9448	$1,018.94	$1,018.95	$1,018.90