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	$180.63	6.241%	$191.9031	$191.90	$191.90	$191.90
Purchase #2	$178.91	9.796%	$196.436	$196.44	$196.45	$196.40
Purchase #3	$70.61	8.406%	$76.5455	$76.55	$76.55	$76.50
Purchase #4	$112.61	13.585%	$127.9081	$127.91	$127.90	$127.90
Purchase #5	$65.60	6.846%	$70.091	$70.09	$70.10	$70.10
Purchase #6	$152.50	13.247%	$172.7017	$172.70	$172.70	$172.70
Purchase #7	$143.87	4.484%	$150.3211	$150.32	$150.30	$150.30
7 purchase totals =	$904.73		$985.9065	$985.91	$985.90	$985.80