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	$220.89	11.453%	$246.1885	$246.19	$246.20	$246.20
Purchase #2	$194.89	12.604%	$219.4539	$219.45	$219.45	$219.50
Purchase #3	$77.98	11.612%	$87.035	$87.04	$87.05	$87.00
Purchase #4	$194.94	5.424%	$205.5135	$205.51	$205.50	$205.50
Purchase #5	$96.67	12.181%	$108.4454	$108.45	$108.45	$108.40
Purchase #6	$165.75	7.764%	$178.6188	$178.62	$178.60	$178.60
Purchase #7	$69.85	12.305%	$78.445	$78.45	$78.45	$78.40
7 purchase totals =	$1,020.97		$1,123.7001	$1,123.71	$1,123.70	$1,123.60