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	$39.55	6.580%	$42.1524	$42.15	$42.15	$42.20
Purchase #2	$183.28	6.304%	$194.834	$194.83	$194.85	$194.80
Purchase #3	$39.58	10.379%	$43.688	$43.69	$43.70	$43.70
Purchase #4	$165.27	4.766%	$173.1468	$173.15	$173.15	$173.10
Purchase #5	$100.79	8.451%	$109.3078	$109.31	$109.30	$109.30
Purchase #6	$142.65	7.195%	$152.9137	$152.91	$152.90	$152.90
Purchase #7	$182.90	6.614%	$194.997	$195.00	$195.00	$195.00
7 purchase totals =	$854.02		$911.0397	$911.04	$911.05	$911.00