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	$25.66	5.438%	$27.0554	$27.06	$27.05	$27.10
Purchase #2	$227.26	7.273%	$243.7886	$243.79	$243.80	$243.80
Purchase #3	$214.33	10.213%	$236.2195	$236.22	$236.20	$236.20
Purchase #4	$138.44	4.184%	$144.2323	$144.23	$144.25	$144.20
Purchase #5	$123.79	3.266%	$127.833	$127.83	$127.85	$127.80
Purchase #6	$42.77	9.159%	$46.6873	$46.69	$46.70	$46.70
Purchase #7	$55.52	6.400%	$59.0733	$59.07	$59.05	$59.10
7 purchase totals =	$827.77		$884.8894	$884.89	$884.90	$884.90