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	$178.27	3.802%	$185.0478	$185.05	$185.05	$185.00
Purchase #2	$38.77	10.424%	$42.8114	$42.81	$42.80	$42.80
Purchase #3	$75.89	12.642%	$85.484	$85.48	$85.50	$85.50
Purchase #4	$224.47	9.244%	$245.22	$245.22	$245.20	$245.20
Purchase #5	$115.74	13.135%	$130.9424	$130.94	$130.95	$130.90
Purchase #6	$165.42	4.275%	$172.4917	$172.49	$172.50	$172.50
Purchase #7	$104.71	9.280%	$114.4271	$114.43	$114.45	$114.40
7 purchase totals =	$903.27		$976.4244	$976.42	$976.45	$976.30