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	$165.52	12.375%	$186.0031	$186.00	$186.00	$186.00
Purchase #2	$66.72	8.277%	$72.2424	$72.24	$72.25	$72.20
Purchase #3	$60.87	9.633%	$66.7336	$66.73	$66.75	$66.70
Purchase #4	$118.75	7.488%	$127.642	$127.64	$127.65	$127.60
Purchase #5	$61.36	6.356%	$65.26	$65.26	$65.25	$65.30
Purchase #6	$64.94	11.252%	$72.247	$72.25	$72.25	$72.20
Purchase #7	$170.55	6.514%	$181.6596	$181.66	$181.65	$181.70
7 purchase totals =	$708.71		$771.7877	$771.78	$771.80	$771.70