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	$234.53	9.647%	$257.1551	$257.16	$257.15	$257.20
Purchase #2	$81.98	13.312%	$92.8932	$92.89	$92.90	$92.90
Purchase #3	$104.61	9.572%	$114.6233	$114.62	$114.60	$114.60
Purchase #4	$31.51	6.311%	$33.4986	$33.50	$33.50	$33.50
Purchase #5	$89.79	11.669%	$100.2676	$100.27	$100.25	$100.30
Purchase #6	$228.57	8.129%	$247.1505	$247.15	$247.15	$247.20
Purchase #7	$86.38	11.707%	$96.4925	$96.49	$96.50	$96.50
7 purchase totals =	$857.37		$942.0808	$942.08	$942.05	$942.20