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	$79.55	4.281%	$82.9555	$82.96	$82.95	$83.00
Purchase #2	$38.51	11.761%	$43.0392	$43.04	$43.05	$43.00
Purchase #3	$10.94	11.626%	$12.2119	$12.21	$12.20	$12.20
Purchase #4	$65.62	11.119%	$72.9163	$72.92	$72.90	$72.90
Purchase #5	$11.85	3.760%	$12.2956	$12.30	$12.30	$12.30
Purchase #6	$157.97	4.547%	$165.1529	$165.15	$165.15	$165.20
Purchase #7	$173.82	10.231%	$191.6035	$191.60	$191.60	$191.60
7 purchase totals =	$538.26		$580.1749	$580.18	$580.15	$580.20