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	$25.68	10.380%	$28.3456	$28.35	$28.35	$28.30
Purchase #2	$211.47	5.820%	$223.7776	$223.78	$223.80	$223.80
Purchase #3	$29.81	6.606%	$31.7792	$31.78	$31.80	$31.80
Purchase #4	$165.41	10.191%	$182.2669	$182.27	$182.25	$182.30
Purchase #5	$147.98	3.275%	$152.8263	$152.83	$152.85	$152.80
Purchase #6	$122.50	9.530%	$134.1743	$134.17	$134.15	$134.20
Purchase #7	$116.80	9.392%	$127.7699	$127.77	$127.75	$127.80
7 purchase totals =	$819.65		$880.9398	$880.95	$880.95	$881.00