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	$157.88	8.606%	$171.4672	$171.47	$171.45	$171.50
Purchase #2	$61.63	4.264%	$64.2579	$64.26	$64.25	$64.30
Purchase #3	$35.43	11.713%	$39.5799	$39.58	$39.60	$39.60
Purchase #4	$100.84	4.303%	$105.1791	$105.18	$105.20	$105.20
Purchase #5	$148.92	4.597%	$155.7659	$155.77	$155.75	$155.80
Purchase #6	$62.90	6.587%	$67.0432	$67.04	$67.05	$67.00
Purchase #7	$158.59	13.443%	$179.9093	$179.91	$179.90	$179.90
7 purchase totals =	$726.19		$783.2025	$783.21	$783.20	$783.30