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	$122.26	4.251%	$127.4573	$127.46	$127.45	$127.50
Purchase #2	$152.27	11.766%	$170.1861	$170.19	$170.20	$170.20
Purchase #3	$60.83	11.447%	$67.7932	$67.79	$67.80	$67.80
Purchase #4	$191.55	10.622%	$211.8964	$211.90	$211.90	$211.90
Purchase #5	$71.80	10.515%	$79.3498	$79.35	$79.35	$79.30
Purchase #6	$190.66	6.521%	$203.0929	$203.09	$203.10	$203.10
Purchase #7	$72.73	8.314%	$78.7768	$78.78	$78.80	$78.80
7 purchase totals =	$862.10		$938.5525	$938.56	$938.60	$938.60