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	$55.94	7.263%	$60.0029	$60.00	$60.00	$60.00
Purchase #2	$157.98	13.674%	$179.5822	$179.58	$179.60	$179.60
Purchase #3	$148.70	13.452%	$168.7031	$168.70	$168.70	$168.70
Purchase #4	$138.85	11.131%	$154.3054	$154.31	$154.30	$154.30
Purchase #5	$228.32	9.373%	$249.7204	$249.72	$249.70	$249.70
Purchase #6	$47.96	5.382%	$50.5412	$50.54	$50.55	$50.50
Purchase #7	$227.64	4.578%	$238.0614	$238.06	$238.05	$238.10
7 purchase totals =	$1,005.39		$1,100.9166	$1,100.91	$1,100.90	$1,100.90