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	$228.38	3.283%	$235.8777	$235.88	$235.90	$235.90
Purchase #2	$108.60	10.577%	$120.0866	$120.09	$120.10	$120.10
Purchase #3	$118.34	10.832%	$131.1586	$131.16	$131.15	$131.20
Purchase #4	$152.28	5.272%	$160.3082	$160.31	$160.30	$160.30
Purchase #5	$28.88	13.804%	$32.8666	$32.87	$32.85	$32.90
Purchase #6	$137.91	9.109%	$150.4722	$150.47	$150.45	$150.50
Purchase #7	$238.35	4.327%	$248.6634	$248.66	$248.65	$248.70
7 purchase totals =	$1,012.74		$1,079.4333	$1,079.44	$1,079.40	$1,079.60