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	$58.43	6.754%	$62.3764	$62.38	$62.40	$62.40
Purchase #2	$117.68	8.405%	$127.571	$127.57	$127.55	$127.60
Purchase #3	$129.64	4.815%	$135.8822	$135.88	$135.90	$135.90
Purchase #4	$40.79	7.492%	$43.846	$43.85	$43.85	$43.80
Purchase #5	$182.38	12.672%	$205.4912	$205.49	$205.50	$205.50
Purchase #6	$192.41	4.356%	$200.7914	$200.79	$200.80	$200.80
Purchase #7	$56.50	10.113%	$62.2138	$62.21	$62.20	$62.20
7 purchase totals =	$777.83		$838.1720	$838.17	$838.20	$838.20