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	$151.39	13.395%	$171.6687	$171.67	$171.65	$171.70
Purchase #2	$80.63	7.296%	$86.5128	$86.51	$86.50	$86.50
Purchase #3	$69.39	11.616%	$77.4503	$77.45	$77.45	$77.50
Purchase #4	$194.35	5.834%	$205.6884	$205.69	$205.70	$205.70
Purchase #5	$80.32	3.235%	$82.9184	$82.92	$82.90	$82.90
Purchase #6	$45.89	13.242%	$51.9668	$51.97	$51.95	$52.00
Purchase #7	$87.89	3.650%	$91.098	$91.10	$91.10	$91.10
7 purchase totals =	$709.86		$767.3034	$767.31	$767.25	$767.40