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	$75.25	3.280%	$77.7182	$77.72	$77.70	$77.70
Purchase #2	$228.90	11.655%	$255.5783	$255.58	$255.60	$255.60
Purchase #3	$48.37	5.131%	$50.8519	$50.85	$50.85	$50.90
Purchase #4	$89.34	6.627%	$95.2606	$95.26	$95.25	$95.30
Purchase #5	$112.71	12.786%	$127.1211	$127.12	$127.10	$127.10
Purchase #6	$22.62	10.572%	$25.0114	$25.01	$25.00	$25.00
Purchase #7	$37.55	10.190%	$41.3763	$41.38	$41.40	$41.40
7 purchase totals =	$614.74		$672.9178	$672.92	$672.90	$673.00