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	$100.69	6.772%	$107.5087	$107.51	$107.50	$107.50
Purchase #2	$92.61	13.858%	$105.4439	$105.44	$105.45	$105.40
Purchase #3	$94.90	9.623%	$104.0322	$104.03	$104.05	$104.00
Purchase #4	$142.50	6.572%	$151.8651	$151.87	$151.85	$151.90
Purchase #5	$131.37	4.202%	$136.8902	$136.89	$136.90	$136.90
Purchase #6	$193.58	13.822%	$220.3366	$220.34	$220.35	$220.30
Purchase #7	$225.31	12.571%	$253.6337	$253.63	$253.65	$253.60
7 purchase totals =	$980.96		$1,079.7104	$1,079.71	$1,079.75	$1,079.60