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	$28.46	12.714%	$32.0784	$32.08	$32.10	$32.10
Purchase #2	$92.51	7.834%	$99.7572	$99.76	$99.75	$99.80
Purchase #3	$163.76	9.231%	$178.8767	$178.88	$178.90	$178.90
Purchase #4	$92.40	13.843%	$105.1909	$105.19	$105.20	$105.20
Purchase #5	$27.70	5.856%	$29.3221	$29.32	$29.30	$29.30
Purchase #6	$125.89	4.438%	$131.477	$131.48	$131.50	$131.50
Purchase #7	$61.80	13.664%	$70.2444	$70.24	$70.25	$70.20
7 purchase totals =	$592.52		$646.9467	$646.95	$647.00	$647.00