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	$60.32	9.614%	$66.1192	$66.12	$66.10	$66.10
Purchase #2	$154.89	11.238%	$172.2965	$172.30	$172.30	$172.30
Purchase #3	$133.56	9.270%	$145.941	$145.94	$145.95	$145.90
Purchase #4	$51.55	6.326%	$54.8111	$54.81	$54.80	$54.80
Purchase #5	$31.42	3.529%	$32.5288	$32.53	$32.55	$32.50
Purchase #6	$99.48	9.327%	$108.7585	$108.76	$108.75	$108.80
Purchase #7	$235.66	6.161%	$250.179	$250.18	$250.20	$250.20
7 purchase totals =	$766.88		$830.6341	$830.64	$830.65	$830.60