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	$217.93	5.353%	$229.5958	$229.60	$229.60	$229.60
Purchase #2	$232.28	7.760%	$250.3049	$250.30	$250.30	$250.30
Purchase #3	$133.61	13.178%	$151.2171	$151.22	$151.20	$151.20
Purchase #4	$185.42	8.179%	$200.5855	$200.59	$200.60	$200.60
Purchase #5	$73.67	11.682%	$82.2761	$82.28	$82.30	$82.30
Purchase #6	$117.98	3.159%	$121.707	$121.71	$121.70	$121.70
Purchase #7	$198.47	11.505%	$221.304	$221.30	$221.30	$221.30
7 purchase totals =	$1,159.36		$1,256.9904	$1,257.00	$1,257.00	$1,257.00