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	$246.81	10.140%	$271.8365	$271.84	$271.85	$271.80
Purchase #2	$85.29	3.715%	$88.4585	$88.46	$88.45	$88.50
Purchase #3	$205.50	10.411%	$226.8946	$226.89	$226.90	$226.90
Purchase #4	$132.34	9.473%	$144.8766	$144.88	$144.90	$144.90
Purchase #5	$200.42	8.326%	$217.107	$217.11	$217.10	$217.10
Purchase #6	$34.87	6.853%	$37.2596	$37.26	$37.25	$37.30
Purchase #7	$105.73	8.137%	$114.3333	$114.33	$114.35	$114.30
7 purchase totals =	$1,010.96		$1,100.7661	$1,100.77	$1,100.80	$1,100.80