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	$118.70	12.572%	$133.623	$133.62	$133.60	$133.60
Purchase #2	$154.25	10.766%	$170.8566	$170.86	$170.85	$170.90
Purchase #3	$56.45	5.850%	$59.7523	$59.75	$59.75	$59.80
Purchase #4	$119.33	12.524%	$134.2749	$134.27	$134.25	$134.30
Purchase #5	$49.26	11.453%	$54.9017	$54.90	$54.90	$54.90
Purchase #6	$157.44	8.803%	$171.2994	$171.30	$171.30	$171.30
Purchase #7	$28.73	13.554%	$32.6241	$32.62	$32.60	$32.60
7 purchase totals =	$684.16		$757.3320	$757.32	$757.25	$757.40