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	$106.79	9.767%	$117.2202	$117.22	$117.20	$117.20
Purchase #2	$116.34	10.681%	$128.7663	$128.77	$128.75	$128.80
Purchase #3	$196.71	7.440%	$211.3452	$211.35	$211.35	$211.30
Purchase #4	$214.64	13.831%	$244.3269	$244.33	$244.35	$244.30
Purchase #5	$28.58	12.467%	$32.1431	$32.14	$32.15	$32.10
Purchase #6	$158.89	5.822%	$168.1406	$168.14	$168.15	$168.10
Purchase #7	$87.93	3.647%	$91.1368	$91.14	$91.15	$91.10
7 purchase totals =	$909.88		$993.0791	$993.09	$993.10	$992.90