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	$72.72	8.374%	$78.8096	$78.81	$78.80	$78.80
Purchase #2	$19.58	3.755%	$20.3152	$20.32	$20.30	$20.30
Purchase #3	$96.74	7.827%	$104.3118	$104.31	$104.30	$104.30
Purchase #4	$207.42	13.251%	$234.9052	$234.91	$234.90	$234.90
Purchase #5	$30.56	5.735%	$32.3126	$32.31	$32.30	$32.30
Purchase #6	$228.83	11.246%	$254.5642	$254.56	$254.55	$254.60
Purchase #7	$167.51	6.210%	$177.9124	$177.91	$177.90	$177.90
7 purchase totals =	$823.36		$903.1310	$903.13	$903.05	$903.10