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	$47.58	3.107%	$49.0583	$49.06	$49.05	$49.10
Purchase #2	$59.34	13.379%	$67.2791	$67.28	$67.30	$67.30
Purchase #3	$24.33	12.339%	$27.3321	$27.33	$27.35	$27.30
Purchase #4	$193.67	6.773%	$206.7873	$206.79	$206.80	$206.80
Purchase #5	$117.84	5.133%	$123.8887	$123.89	$123.90	$123.90
Purchase #6	$131.54	10.269%	$145.0478	$145.05	$145.05	$145.00
Purchase #7	$191.54	4.729%	$200.5979	$200.60	$200.60	$200.60
7 purchase totals =	$765.84		$819.9912	$820.00	$820.05	$820.00