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	$100.52	6.726%	$107.281	$107.28	$107.30	$107.30
Purchase #2	$94.62	6.340%	$100.6189	$100.62	$100.60	$100.60
Purchase #3	$75.36	12.425%	$84.7235	$84.72	$84.70	$84.70
Purchase #4	$149.29	12.826%	$168.4379	$168.44	$168.45	$168.40
Purchase #5	$242.88	9.377%	$265.6549	$265.65	$265.65	$265.70
Purchase #6	$120.51	5.769%	$127.4622	$127.46	$127.45	$127.50
Purchase #7	$128.87	12.426%	$144.8834	$144.88	$144.90	$144.90
7 purchase totals =	$912.05		$999.0618	$999.05	$999.05	$999.10