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	$250.76	5.304%	$264.0603	$264.06	$264.05	$264.10
Purchase #2	$158.59	8.689%	$172.3699	$172.37	$172.35	$172.40
Purchase #3	$183.61	8.313%	$198.8735	$198.87	$198.85	$198.90
Purchase #4	$160.39	8.485%	$173.9991	$174.00	$174.00	$174.00
Purchase #5	$137.81	12.308%	$154.7717	$154.77	$154.75	$154.80
Purchase #6	$35.45	7.114%	$37.9719	$37.97	$37.95	$38.00
Purchase #7	$36.80	10.860%	$40.7965	$40.80	$40.80	$40.80
7 purchase totals =	$963.41		$1,042.8429	$1,042.84	$1,042.75	$1,043.00