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	$106.27	10.642%	$117.5793	$117.58	$117.60	$117.60
Purchase #2	$128.87	10.793%	$142.7789	$142.78	$142.80	$142.80
Purchase #3	$19.35	5.365%	$20.3881	$20.39	$20.40	$20.40
Purchase #4	$137.94	9.772%	$151.4195	$151.42	$151.40	$151.40
Purchase #5	$148.66	13.625%	$168.9149	$168.91	$168.90	$168.90
Purchase #6	$179.64	6.521%	$191.3543	$191.35	$191.35	$191.40
Purchase #7	$40.60	11.606%	$45.312	$45.31	$45.30	$45.30
7 purchase totals =	$761.33		$837.7470	$837.74	$837.75	$837.80