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	$20.29	11.208%	$22.5641	$22.56	$22.55	$22.60
Purchase #2	$180.29	5.456%	$190.1266	$190.13	$190.15	$190.10
Purchase #3	$166.58	9.340%	$182.1386	$182.14	$182.15	$182.10
Purchase #4	$231.69	11.632%	$258.6402	$258.64	$258.65	$258.60
Purchase #5	$143.60	5.702%	$151.7881	$151.79	$151.80	$151.80
Purchase #6	$168.25	13.691%	$191.2851	$191.29	$191.30	$191.30
Purchase #7	$6.69	8.440%	$7.2546	$7.25	$7.25	$7.30
7 purchase totals =	$917.39		$1,003.7973	$1,003.80	$1,003.85	$1,003.80