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	$98.58	9.652%	$108.0949	$108.09	$108.10	$108.10
Purchase #2	$85.65	5.439%	$90.3085	$90.31	$90.30	$90.30
Purchase #3	$191.89	12.157%	$215.2181	$215.22	$215.20	$215.20
Purchase #4	$195.83	7.400%	$210.3214	$210.32	$210.30	$210.30
Purchase #5	$141.47	12.196%	$158.7237	$158.72	$158.70	$158.70
Purchase #6	$109.61	4.459%	$114.4975	$114.50	$114.50	$114.50
Purchase #7	$177.31	10.401%	$195.752	$195.75	$195.75	$195.80
7 purchase totals =	$1,000.34		$1,092.9161	$1,092.91	$1,092.85	$1,092.90