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	$18.82	9.400%	$20.5891	$20.59	$20.60	$20.60
Purchase #2	$241.72	8.751%	$262.8729	$262.87	$262.85	$262.90
Purchase #3	$10.76	3.506%	$11.1372	$11.14	$11.15	$11.10
Purchase #4	$127.73	10.611%	$141.2834	$141.28	$141.30	$141.30
Purchase #5	$131.39	4.608%	$137.4445	$137.44	$137.45	$137.40
Purchase #6	$160.53	9.559%	$175.8751	$175.88	$175.90	$175.90
Purchase #7	$155.90	9.841%	$171.2421	$171.24	$171.25	$171.20
7 purchase totals =	$846.85		$920.4443	$920.44	$920.50	$920.40