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	$100.35	13.467%	$113.8641	$113.86	$113.85	$113.90
Purchase #2	$167.68	7.399%	$180.0866	$180.09	$180.10	$180.10
Purchase #3	$123.97	8.314%	$134.2769	$134.28	$134.30	$134.30
Purchase #4	$77.82	11.603%	$86.8495	$86.85	$86.85	$86.80
Purchase #5	$59.64	3.289%	$61.6016	$61.60	$61.60	$61.60
Purchase #6	$220.92	5.581%	$233.2495	$233.25	$233.25	$233.20
Purchase #7	$141.78	10.599%	$156.8073	$156.81	$156.80	$156.80
7 purchase totals =	$892.16		$966.7355	$966.74	$966.75	$966.70