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	$198.61	6.831%	$212.177	$212.18	$212.20	$212.20
Purchase #2	$153.56	3.819%	$159.4245	$159.42	$159.40	$159.40
Purchase #3	$143.87	6.216%	$152.813	$152.81	$152.80	$152.80
Purchase #4	$56.38	10.814%	$62.4769	$62.48	$62.50	$62.50
Purchase #5	$116.53	9.866%	$128.0268	$128.03	$128.05	$128.00
Purchase #6	$83.59	6.271%	$88.8319	$88.83	$88.85	$88.80
Purchase #7	$81.53	10.760%	$90.3026	$90.30	$90.30	$90.30
7 purchase totals =	$834.07		$894.0527	$894.05	$894.10	$894.00