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	$93.47	6.846%	$99.869	$99.87	$99.85	$99.90
Purchase #2	$114.47	11.765%	$127.9374	$127.94	$127.95	$127.90
Purchase #3	$180.32	9.191%	$196.8932	$196.89	$196.90	$196.90
Purchase #4	$78.76	8.389%	$85.3672	$85.37	$85.35	$85.40
Purchase #5	$137.97	11.271%	$153.5206	$153.52	$153.50	$153.50
Purchase #6	$241.33	6.458%	$256.9151	$256.92	$256.90	$256.90
Purchase #7	$81.72	13.687%	$92.905	$92.91	$92.90	$92.90
7 purchase totals =	$928.04		$1,013.4075	$1,013.42	$1,013.35	$1,013.40