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	$53.33	6.693%	$56.8994	$56.90	$56.90	$56.90
Purchase #2	$238.92	7.112%	$255.912	$255.91	$255.90	$255.90
Purchase #3	$67.63	6.579%	$72.0794	$72.08	$72.10	$72.10
Purchase #4	$113.48	13.409%	$128.6965	$128.70	$128.70	$128.70
Purchase #5	$167.62	3.737%	$173.884	$173.88	$173.90	$173.90
Purchase #6	$121.60	13.163%	$137.6062	$137.61	$137.60	$137.60
Purchase #7	$179.70	8.527%	$195.023	$195.02	$195.00	$195.00
7 purchase totals =	$942.28		$1,020.1005	$1,020.10	$1,020.10	$1,020.10