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	$79.80	13.632%	$90.6783	$90.68	$90.70	$90.70
Purchase #2	$106.66	4.253%	$111.1962	$111.20	$111.20	$111.20
Purchase #3	$166.78	10.229%	$183.8399	$183.84	$183.85	$183.80
Purchase #4	$78.71	4.200%	$82.0158	$82.02	$82.00	$82.00
Purchase #5	$247.94	4.320%	$258.651	$258.65	$258.65	$258.70
Purchase #6	$6.76	8.168%	$7.3122	$7.31	$7.30	$7.30
Purchase #7	$250.31	13.549%	$284.2245	$284.22	$284.20	$284.20
7 purchase totals =	$936.96		$1,017.9179	$1,017.92	$1,017.90	$1,017.90