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	$90.28	10.230%	$99.5156	$99.52	$99.50	$99.50
Purchase #2	$123.90	9.271%	$135.3868	$135.39	$135.40	$135.40
Purchase #3	$19.63	9.509%	$21.4966	$21.50	$21.50	$21.50
Purchase #4	$246.33	10.669%	$272.6109	$272.61	$272.60	$272.60
Purchase #5	$220.95	12.835%	$249.3089	$249.31	$249.30	$249.30
Purchase #6	$244.83	11.514%	$273.0197	$273.02	$273.00	$273.00
Purchase #7	$151.31	9.548%	$165.7571	$165.76	$165.75	$165.80
7 purchase totals =	$1,097.23		$1,217.0956	$1,217.11	$1,217.05	$1,217.10