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	$86.91	13.783%	$98.8888	$98.89	$98.90	$98.90
Purchase #2	$81.31	12.273%	$91.2892	$91.29	$91.30	$91.30
Purchase #3	$92.58	10.280%	$102.0972	$102.10	$102.10	$102.10
Purchase #4	$34.30	8.810%	$37.3218	$37.32	$37.30	$37.30
Purchase #5	$39.36	4.813%	$41.2544	$41.25	$41.25	$41.30
Purchase #6	$101.43	12.255%	$113.8602	$113.86	$113.85	$113.90
Purchase #7	$56.47	11.137%	$62.7591	$62.76	$62.75	$62.80
7 purchase totals =	$492.36		$547.4707	$547.47	$547.45	$547.60