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	$138.87	6.236%	$147.5299	$147.53	$147.55	$147.50
Purchase #2	$133.48	13.840%	$151.9536	$151.95	$151.95	$152.00
Purchase #3	$150.51	7.748%	$162.1715	$162.17	$162.15	$162.20
Purchase #4	$238.54	11.444%	$265.8385	$265.84	$265.85	$265.80
Purchase #5	$246.82	6.397%	$262.6091	$262.61	$262.60	$262.60
Purchase #6	$74.48	13.581%	$84.5951	$84.60	$84.60	$84.60
Purchase #7	$190.35	5.380%	$200.5908	$200.59	$200.60	$200.60
7 purchase totals =	$1,173.05		$1,275.2885	$1,275.29	$1,275.30	$1,275.30