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	$72.65	12.396%	$81.6557	$81.66	$81.65	$81.70
Purchase #2	$9.58	13.186%	$10.8432	$10.84	$10.85	$10.80
Purchase #3	$247.95	11.267%	$275.8865	$275.89	$275.90	$275.90
Purchase #4	$47.76	7.466%	$51.3258	$51.33	$51.35	$51.30
Purchase #5	$185.34	11.418%	$206.5021	$206.50	$206.50	$206.50
Purchase #6	$116.86	9.571%	$128.0447	$128.04	$128.05	$128.00
Purchase #7	$57.72	3.521%	$59.7523	$59.75	$59.75	$59.80
7 purchase totals =	$737.86		$814.0103	$814.01	$814.05	$814.00