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	$197.99	6.207%	$210.2792	$210.28	$210.30	$210.30
Purchase #2	$81.92	9.395%	$89.6164	$89.62	$89.60	$89.60
Purchase #3	$231.51	7.826%	$249.628	$249.63	$249.65	$249.60
Purchase #4	$231.97	4.255%	$241.8403	$241.84	$241.85	$241.80
Purchase #5	$78.89	8.221%	$85.3755	$85.38	$85.40	$85.40
Purchase #6	$189.72	12.223%	$212.9095	$212.91	$212.90	$212.90
Purchase #7	$97.89	11.252%	$108.9046	$108.90	$108.90	$108.90
7 purchase totals =	$1,109.89		$1,198.5535	$1,198.56	$1,198.60	$1,198.50