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	$16.58	7.777%	$17.8694	$17.87	$17.85	$17.90
Purchase #2	$179.64	8.211%	$194.3902	$194.39	$194.40	$194.40
Purchase #3	$116.34	10.144%	$128.1415	$128.14	$128.15	$128.10
Purchase #4	$100.54	11.602%	$112.2047	$112.20	$112.20	$112.20
Purchase #5	$83.85	8.400%	$90.8934	$90.89	$90.90	$90.90
Purchase #6	$123.92	9.831%	$136.1026	$136.10	$136.10	$136.10
Purchase #7	$115.32	11.614%	$128.7133	$128.71	$128.70	$128.70
7 purchase totals =	$736.19		$808.3151	$808.30	$808.30	$808.30