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	$79.71	12.323%	$89.5327	$89.53	$89.55	$89.50
Purchase #2	$17.29	10.434%	$19.094	$19.09	$19.10	$19.10
Purchase #3	$67.92	7.368%	$72.9243	$72.92	$72.90	$72.90
Purchase #4	$131.39	5.659%	$138.8254	$138.83	$138.85	$138.80
Purchase #5	$59.37	12.516%	$66.8007	$66.80	$66.80	$66.80
Purchase #6	$166.67	10.202%	$183.6737	$183.67	$183.65	$183.70
Purchase #7	$213.92	10.505%	$236.3923	$236.39	$236.40	$236.40
7 purchase totals =	$736.27		$807.2431	$807.23	$807.25	$807.20