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	$18.38	11.366%	$20.4691	$20.47	$20.45	$20.50
Purchase #2	$125.97	3.326%	$130.1598	$130.16	$130.15	$130.20
Purchase #3	$123.72	6.786%	$132.1156	$132.12	$132.10	$132.10
Purchase #4	$53.63	7.140%	$57.4592	$57.46	$57.45	$57.50
Purchase #5	$125.77	9.632%	$137.8842	$137.88	$137.90	$137.90
Purchase #6	$178.55	11.448%	$198.9904	$198.99	$199.00	$199.00
Purchase #7	$93.84	5.869%	$99.3475	$99.35	$99.35	$99.30
7 purchase totals =	$719.86		$776.4258	$776.43	$776.40	$776.50