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	$127.92	10.866%	$141.8198	$141.82	$141.80	$141.80
Purchase #2	$199.67	11.715%	$223.0613	$223.06	$223.05	$223.10
Purchase #3	$50.83	10.681%	$56.2592	$56.26	$56.25	$56.30
Purchase #4	$41.53	8.661%	$45.1269	$45.13	$45.15	$45.10
Purchase #5	$37.52	4.490%	$39.2046	$39.20	$39.20	$39.20
Purchase #6	$132.30	7.216%	$141.8468	$141.85	$141.85	$141.80
Purchase #7	$5.48	9.691%	$6.0111	$6.01	$6.00	$6.00
7 purchase totals =	$595.25		$653.3297	$653.33	$653.30	$653.30