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	$178.72	5.812%	$189.1072	$189.11	$189.10	$189.10
Purchase #2	$243.51	3.410%	$251.8137	$251.81	$251.80	$251.80
Purchase #3	$64.87	9.603%	$71.0995	$71.10	$71.10	$71.10
Purchase #4	$158.42	7.155%	$169.755	$169.76	$169.75	$169.80
Purchase #5	$199.71	6.233%	$212.1579	$212.16	$212.15	$212.20
Purchase #6	$167.78	7.778%	$180.8299	$180.83	$180.85	$180.80
Purchase #7	$50.94	3.794%	$52.8727	$52.87	$52.85	$52.90
7 purchase totals =	$1,063.95		$1,127.6359	$1,127.64	$1,127.60	$1,127.70