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	$213.80	13.712%	$243.1163	$243.12	$243.10	$243.10
Purchase #2	$208.36	9.591%	$228.3438	$228.34	$228.35	$228.30
Purchase #3	$80.51	6.191%	$85.4944	$85.49	$85.50	$85.50
Purchase #4	$52.29	7.370%	$56.1438	$56.14	$56.15	$56.10
Purchase #5	$14.28	4.540%	$14.9283	$14.93	$14.95	$14.90
Purchase #6	$38.84	9.416%	$42.4972	$42.50	$42.50	$42.50
Purchase #7	$137.61	6.144%	$146.0648	$146.06	$146.05	$146.10
7 purchase totals =	$745.69		$816.5886	$816.58	$816.60	$816.50