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	$52.51	4.670%	$54.9622	$54.96	$54.95	$55.00
Purchase #2	$226.73	11.611%	$253.0556	$253.06	$253.05	$253.10
Purchase #3	$225.85	4.280%	$235.5164	$235.52	$235.50	$235.50
Purchase #4	$211.93	10.369%	$233.905	$233.91	$233.90	$233.90
Purchase #5	$75.69	9.318%	$82.7428	$82.74	$82.75	$82.70
Purchase #6	$138.57	8.491%	$150.336	$150.34	$150.35	$150.30
Purchase #7	$119.93	6.574%	$127.8142	$127.81	$127.80	$127.80
7 purchase totals =	$1,051.21		$1,138.3322	$1,138.34	$1,138.30	$1,138.30