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	$64.45	10.311%	$71.0954	$71.10	$71.10	$71.10
Purchase #2	$180.26	4.747%	$188.8169	$188.82	$188.80	$188.80
Purchase #3	$105.76	3.535%	$109.4986	$109.50	$109.50	$109.50
Purchase #4	$218.35	11.661%	$243.8118	$243.81	$243.80	$243.80
Purchase #5	$240.44	7.852%	$259.3193	$259.32	$259.30	$259.30
Purchase #6	$122.68	6.239%	$130.334	$130.33	$130.35	$130.30
Purchase #7	$69.34	13.379%	$78.617	$78.62	$78.60	$78.60
7 purchase totals =	$1,001.28		$1,081.4930	$1,081.50	$1,081.45	$1,081.40