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	$220.49	6.566%	$234.9674	$234.97	$234.95	$235.00
Purchase #2	$118.92	10.597%	$131.522	$131.52	$131.50	$131.50
Purchase #3	$52.25	12.493%	$58.7776	$58.78	$58.80	$58.80
Purchase #4	$42.39	10.722%	$46.9351	$46.94	$46.95	$46.90
Purchase #5	$59.72	8.322%	$64.6899	$64.69	$64.70	$64.70
Purchase #6	$249.52	8.498%	$270.7242	$270.72	$270.70	$270.70
Purchase #7	$152.97	10.389%	$168.8621	$168.86	$168.85	$168.90
7 purchase totals =	$896.26		$976.4783	$976.48	$976.45	$976.50