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	$25.33	11.162%	$28.1573	$28.16	$28.15	$28.20
Purchase #2	$189.86	9.810%	$208.4853	$208.49	$208.50	$208.50
Purchase #3	$50.88	10.627%	$56.287	$56.29	$56.30	$56.30
Purchase #4	$250.49	10.418%	$276.586	$276.59	$276.60	$276.60
Purchase #5	$103.78	5.397%	$109.381	$109.38	$109.40	$109.40
Purchase #6	$119.76	12.662%	$134.924	$134.92	$134.90	$134.90
Purchase #7	$145.88	11.689%	$162.9319	$162.93	$162.95	$162.90
7 purchase totals =	$885.98		$976.7525	$976.76	$976.80	$976.80