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	$11.25	11.266%	$12.5174	$12.52	$12.50	$12.50
Purchase #2	$30.87	9.813%	$33.8993	$33.90	$33.90	$33.90
Purchase #3	$109.78	5.699%	$116.0364	$116.04	$116.05	$116.00
Purchase #4	$82.59	6.736%	$88.1533	$88.15	$88.15	$88.20
Purchase #5	$124.45	3.398%	$128.6788	$128.68	$128.70	$128.70
Purchase #6	$141.38	4.591%	$147.8708	$147.87	$147.85	$147.90
Purchase #7	$105.31	6.234%	$111.875	$111.88	$111.90	$111.90
7 purchase totals =	$605.63		$639.0310	$639.04	$639.05	$639.10