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	$87.32	3.638%	$90.4967	$90.50	$90.50	$90.50
Purchase #2	$35.84	9.137%	$39.1147	$39.11	$39.10	$39.10
Purchase #3	$86.98	11.145%	$96.6739	$96.67	$96.65	$96.70
Purchase #4	$54.75	3.543%	$56.6898	$56.69	$56.70	$56.70
Purchase #5	$232.54	6.238%	$247.0458	$247.05	$247.05	$247.00
Purchase #6	$241.38	9.309%	$263.8501	$263.85	$263.85	$263.90
Purchase #7	$175.59	5.697%	$185.5934	$185.59	$185.60	$185.60
7 purchase totals =	$914.40		$979.4644	$979.46	$979.45	$979.50