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	$34.41	7.538%	$37.0038	$37.00	$37.00	$37.00
Purchase #2	$36.81	13.619%	$41.8232	$41.82	$41.80	$41.80
Purchase #3	$196.83	3.302%	$203.3293	$203.33	$203.35	$203.30
Purchase #4	$91.47	8.467%	$99.2148	$99.21	$99.20	$99.20
Purchase #5	$50.51	4.153%	$52.6077	$52.61	$52.60	$52.60
Purchase #6	$89.55	10.740%	$99.1677	$99.17	$99.15	$99.20
Purchase #7	$83.38	6.643%	$88.9189	$88.92	$88.90	$88.90
7 purchase totals =	$582.96		$622.0654	$622.06	$622.00	$622.00