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	$73.77	6.841%	$78.8166	$78.82	$78.80	$78.80
Purchase #2	$145.87	12.834%	$164.591	$164.59	$164.60	$164.60
Purchase #3	$6.84	9.758%	$7.5074	$7.51	$7.50	$7.50
Purchase #4	$184.94	9.397%	$202.3188	$202.32	$202.30	$202.30
Purchase #5	$50.28	5.278%	$52.9338	$52.93	$52.95	$52.90
Purchase #6	$13.27	9.512%	$14.5322	$14.53	$14.55	$14.50
Purchase #7	$156.68	6.108%	$166.25	$166.25	$166.25	$166.30
7 purchase totals =	$631.65		$686.9498	$686.95	$686.95	$686.90