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	$30.75	6.580%	$32.7734	$32.77	$32.75	$32.80
Purchase #2	$125.60	4.229%	$130.9116	$130.91	$130.90	$130.90
Purchase #3	$126.35	13.282%	$143.1318	$143.13	$143.15	$143.10
Purchase #4	$79.73	13.689%	$90.6442	$90.64	$90.65	$90.60
Purchase #5	$47.89	8.203%	$51.8184	$51.82	$51.80	$51.80
Purchase #6	$5.41	5.223%	$5.6926	$5.69	$5.70	$5.70
Purchase #7	$90.26	9.745%	$99.0558	$99.06	$99.05	$99.10
7 purchase totals =	$505.99		$554.0278	$554.02	$554.00	$554.00