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	$29.52	11.734%	$32.9839	$32.98	$33.00	$33.00
Purchase #2	$191.73	11.719%	$214.1988	$214.20	$214.20	$214.20
Purchase #3	$235.46	9.787%	$258.5045	$258.50	$258.50	$258.50
Purchase #4	$123.67	10.870%	$137.1129	$137.11	$137.10	$137.10
Purchase #5	$27.86	10.874%	$30.8895	$30.89	$30.90	$30.90
Purchase #6	$200.88	13.165%	$227.3259	$227.33	$227.35	$227.30
Purchase #7	$100.60	6.821%	$107.4619	$107.46	$107.45	$107.50
7 purchase totals =	$909.72		$1,008.4774	$1,008.47	$1,008.50	$1,008.50