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	$39.32	11.453%	$43.8233	$43.82	$43.80	$43.80
Purchase #2	$97.99	7.210%	$105.0551	$105.06	$105.05	$105.10
Purchase #3	$98.37	11.572%	$109.7534	$109.75	$109.75	$109.80
Purchase #4	$200.33	7.237%	$214.8279	$214.83	$214.85	$214.80
Purchase #5	$192.31	10.319%	$212.1545	$212.15	$212.15	$212.20
Purchase #6	$111.84	7.266%	$119.9663	$119.97	$119.95	$120.00
Purchase #7	$57.32	13.842%	$65.2542	$65.25	$65.25	$65.30
7 purchase totals =	$797.48		$870.8347	$870.83	$870.80	$871.00