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	$155.89	9.229%	$170.2771	$170.28	$170.30	$170.30
Purchase #2	$165.49	3.769%	$171.7273	$171.73	$171.75	$171.70
Purchase #3	$139.84	8.559%	$151.8089	$151.81	$151.80	$151.80
Purchase #4	$140.32	13.233%	$158.8885	$158.89	$158.90	$158.90
Purchase #5	$176.46	13.614%	$200.4833	$200.48	$200.50	$200.50
Purchase #6	$61.82	4.400%	$64.5401	$64.54	$64.55	$64.50
Purchase #7	$59.57	5.200%	$62.6676	$62.67	$62.65	$62.70
7 purchase totals =	$899.39		$980.3928	$980.40	$980.45	$980.40