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	$85.47	6.330%	$90.8803	$90.88	$90.90	$90.90
Purchase #2	$47.60	5.383%	$50.1623	$50.16	$50.15	$50.20
Purchase #3	$117.33	13.648%	$133.3432	$133.34	$133.35	$133.30
Purchase #4	$174.80	6.422%	$186.0257	$186.03	$186.05	$186.00
Purchase #5	$242.31	13.836%	$275.836	$275.84	$275.85	$275.80
Purchase #6	$215.49	6.456%	$229.402	$229.40	$229.40	$229.40
Purchase #7	$28.91	13.176%	$32.7192	$32.72	$32.70	$32.70
7 purchase totals =	$911.91		$998.3687	$998.37	$998.40	$998.30