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	$205.41	6.487%	$218.7349	$218.73	$218.75	$218.70
Purchase #2	$155.86	5.246%	$164.0364	$164.04	$164.05	$164.00
Purchase #3	$127.93	7.462%	$137.4761	$137.48	$137.50	$137.50
Purchase #4	$151.71	3.200%	$156.5647	$156.56	$156.55	$156.60
Purchase #5	$79.90	3.151%	$82.4176	$82.42	$82.40	$82.40
Purchase #6	$57.46	6.443%	$61.1621	$61.16	$61.15	$61.20
Purchase #7	$11.25	11.444%	$12.5375	$12.54	$12.55	$12.50
7 purchase totals =	$789.52		$832.9293	$832.93	$832.95	$832.90