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	$25.61	6.663%	$27.3164	$27.32	$27.30	$27.30
Purchase #2	$47.95	9.434%	$52.4736	$52.47	$52.45	$52.50
Purchase #3	$32.62	12.307%	$36.6345	$36.63	$36.65	$36.60
Purchase #4	$50.89	10.690%	$56.3301	$56.33	$56.35	$56.30
Purchase #5	$79.48	10.224%	$87.606	$87.61	$87.60	$87.60
Purchase #6	$114.99	11.308%	$127.9931	$127.99	$128.00	$128.00
Purchase #7	$21.42	6.842%	$22.8856	$22.89	$22.90	$22.90
7 purchase totals =	$372.96		$411.2393	$411.24	$411.25	$411.20