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	$59.27	12.853%	$66.888	$66.89	$66.90	$66.90
Purchase #2	$83.30	9.147%	$90.9195	$90.92	$90.90	$90.90
Purchase #3	$188.51	11.496%	$210.1811	$210.18	$210.20	$210.20
Purchase #4	$241.57	10.438%	$266.7851	$266.79	$266.80	$266.80
Purchase #5	$70.93	10.435%	$78.3315	$78.33	$78.35	$78.30
Purchase #6	$24.74	4.372%	$25.8216	$25.82	$25.80	$25.80
Purchase #7	$12.36	4.410%	$12.9051	$12.91	$12.90	$12.90
7 purchase totals =	$680.68		$751.8319	$751.84	$751.85	$751.80