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	$70.50	6.525%	$75.1001	$75.10	$75.10	$75.10
Purchase #2	$55.53	12.661%	$62.5607	$62.56	$62.55	$62.60
Purchase #3	$196.98	12.560%	$221.7207	$221.72	$221.70	$221.70
Purchase #4	$146.46	4.202%	$152.6142	$152.61	$152.60	$152.60
Purchase #5	$225.42	6.187%	$239.3667	$239.37	$239.35	$239.40
Purchase #6	$37.53	12.356%	$42.1672	$42.17	$42.15	$42.20
Purchase #7	$218.85	10.690%	$242.2451	$242.25	$242.25	$242.20
7 purchase totals =	$951.27		$1,035.7747	$1,035.78	$1,035.70	$1,035.80