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	$227.28	10.832%	$251.899	$251.90	$251.90	$251.90
Purchase #2	$224.59	5.862%	$237.7555	$237.76	$237.75	$237.80
Purchase #3	$156.87	4.150%	$163.3801	$163.38	$163.40	$163.40
Purchase #4	$154.71	13.504%	$175.602	$175.60	$175.60	$175.60
Purchase #5	$80.81	10.306%	$89.1383	$89.14	$89.15	$89.10
Purchase #6	$89.56	8.119%	$96.8314	$96.83	$96.85	$96.80
Purchase #7	$73.39	6.576%	$78.2161	$78.22	$78.20	$78.20
7 purchase totals =	$1,007.21		$1,092.8224	$1,092.83	$1,092.85	$1,092.80