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	$77.32	6.335%	$82.2182	$82.22	$82.20	$82.20
Purchase #2	$137.71	4.504%	$143.9125	$143.91	$143.90	$143.90
Purchase #3	$17.81	3.383%	$18.4125	$18.41	$18.40	$18.40
Purchase #4	$171.74	11.367%	$191.2617	$191.26	$191.25	$191.30
Purchase #5	$50.76	13.853%	$57.7918	$57.79	$57.80	$57.80
Purchase #6	$227.59	5.795%	$240.7788	$240.78	$240.80	$240.80
Purchase #7	$156.84	13.749%	$178.4039	$178.40	$178.40	$178.40
7 purchase totals =	$839.77		$912.7794	$912.77	$912.75	$912.80