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	$172.41	11.438%	$192.1303	$192.13	$192.15	$192.10
Purchase #2	$121.86	5.404%	$128.4453	$128.45	$128.45	$128.40
Purchase #3	$145.72	3.179%	$150.3524	$150.35	$150.35	$150.40
Purchase #4	$223.77	6.278%	$237.8183	$237.82	$237.80	$237.80
Purchase #5	$217.51	9.769%	$238.7586	$238.76	$238.75	$238.80
Purchase #6	$79.89	4.705%	$83.6488	$83.65	$83.65	$83.60
Purchase #7	$78.45	12.574%	$88.3143	$88.31	$88.30	$88.30
7 purchase totals =	$1,039.61		$1,119.4680	$1,119.47	$1,119.45	$1,119.40