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	$146.54	10.214%	$161.5076	$161.51	$161.50	$161.50
Purchase #2	$100.35	8.804%	$109.1848	$109.18	$109.20	$109.20
Purchase #3	$91.27	4.548%	$95.421	$95.42	$95.40	$95.40
Purchase #4	$10.25	13.706%	$11.6549	$11.65	$11.65	$11.70
Purchase #5	$51.59	9.582%	$56.5334	$56.53	$56.55	$56.50
Purchase #6	$123.34	6.637%	$131.5261	$131.53	$131.55	$131.50
Purchase #7	$198.50	12.349%	$223.0128	$223.01	$223.00	$223.00
7 purchase totals =	$721.84		$788.8406	$788.83	$788.85	$788.80