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	$250.36	11.355%	$278.7884	$278.79	$278.80	$278.80
Purchase #2	$57.62	6.869%	$61.5779	$61.58	$61.60	$61.60
Purchase #3	$19.60	6.686%	$20.9105	$20.91	$20.90	$20.90
Purchase #4	$56.59	9.621%	$62.0345	$62.03	$62.05	$62.00
Purchase #5	$235.59	3.209%	$243.1501	$243.15	$243.15	$243.20
Purchase #6	$62.62	10.471%	$69.1769	$69.18	$69.20	$69.20
Purchase #7	$116.63	9.606%	$127.8335	$127.83	$127.85	$127.80
7 purchase totals =	$799.01		$863.4718	$863.47	$863.55	$863.50