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	$52.96	8.654%	$57.5432	$57.54	$57.55	$57.50
Purchase #2	$128.71	13.322%	$145.8567	$145.86	$145.85	$145.90
Purchase #3	$184.65	4.792%	$193.4984	$193.50	$193.50	$193.50
Purchase #4	$60.34	6.565%	$64.3013	$64.30	$64.30	$64.30
Purchase #5	$132.70	4.256%	$138.3477	$138.35	$138.35	$138.30
Purchase #6	$47.31	9.673%	$51.8863	$51.89	$51.90	$51.90
Purchase #7	$173.49	7.114%	$185.8321	$185.83	$185.85	$185.80
7 purchase totals =	$780.16		$837.2657	$837.27	$837.30	$837.20