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	$144.86	6.221%	$153.8717	$153.87	$153.85	$153.90
Purchase #2	$108.59	5.613%	$114.6852	$114.69	$114.70	$114.70
Purchase #3	$189.74	13.815%	$215.9526	$215.95	$215.95	$216.00
Purchase #4	$78.52	4.785%	$82.2772	$82.28	$82.30	$82.30
Purchase #5	$116.70	7.596%	$125.5645	$125.56	$125.55	$125.60
Purchase #6	$28.85	11.594%	$32.1949	$32.19	$32.20	$32.20
Purchase #7	$87.82	12.604%	$98.8888	$98.89	$98.90	$98.90
7 purchase totals =	$755.08		$823.4349	$823.43	$823.45	$823.60