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	$83.60	9.574%	$91.6039	$91.60	$91.60	$91.60
Purchase #2	$52.25	8.260%	$56.5659	$56.57	$56.55	$56.60
Purchase #3	$151.34	5.234%	$159.2611	$159.26	$159.25	$159.30
Purchase #4	$218.84	10.655%	$242.1574	$242.16	$242.15	$242.20
Purchase #5	$90.69	5.260%	$95.4603	$95.46	$95.45	$95.50
Purchase #6	$218.72	12.439%	$245.9266	$245.93	$245.95	$245.90
Purchase #7	$132.25	8.502%	$143.4939	$143.49	$143.50	$143.50
7 purchase totals =	$947.69		$1,034.4691	$1,034.47	$1,034.45	$1,034.60