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	$202.54	5.114%	$212.8979	$212.90	$212.90	$212.90
Purchase #2	$113.35	10.193%	$124.9038	$124.90	$124.90	$124.90
Purchase #3	$133.85	6.731%	$142.8594	$142.86	$142.85	$142.90
Purchase #4	$42.86	9.253%	$46.8258	$46.83	$46.85	$46.80
Purchase #5	$64.45	7.671%	$69.394	$69.39	$69.40	$69.40
Purchase #6	$149.35	11.159%	$166.016	$166.02	$166.00	$166.00
Purchase #7	$114.47	11.186%	$127.2746	$127.27	$127.25	$127.30
7 purchase totals =	$820.87		$890.1715	$890.17	$890.15	$890.20