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	$21.51	3.637%	$22.2923	$22.29	$22.30	$22.30
Purchase #2	$110.49	12.108%	$123.8681	$123.87	$123.85	$123.90
Purchase #3	$224.64	7.382%	$241.2229	$241.22	$241.20	$241.20
Purchase #4	$191.69	5.640%	$202.5013	$202.50	$202.50	$202.50
Purchase #5	$105.25	10.429%	$116.2265	$116.23	$116.25	$116.20
Purchase #6	$98.54	4.336%	$102.8127	$102.81	$102.80	$102.80
Purchase #7	$89.61	7.787%	$96.5879	$96.59	$96.60	$96.60
7 purchase totals =	$841.73		$905.5117	$905.51	$905.50	$905.50