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	$83.64	9.507%	$91.5917	$91.59	$91.60	$91.60
Purchase #2	$51.86	6.376%	$55.1666	$55.17	$55.15	$55.20
Purchase #3	$221.32	8.650%	$240.4642	$240.46	$240.45	$240.50
Purchase #4	$165.99	4.693%	$173.7799	$173.78	$173.80	$173.80
Purchase #5	$134.56	4.551%	$140.6838	$140.68	$140.70	$140.70
Purchase #6	$69.75	3.429%	$72.1417	$72.14	$72.15	$72.10
Purchase #7	$100.25	3.211%	$103.469	$103.47	$103.45	$103.50
7 purchase totals =	$827.37		$877.2969	$877.29	$877.30	$877.40