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	$211.82	5.622%	$223.7285	$223.73	$223.75	$223.70
Purchase #2	$82.32	9.201%	$89.8943	$89.89	$89.90	$89.90
Purchase #3	$209.55	8.792%	$227.9736	$227.97	$227.95	$228.00
Purchase #4	$20.27	6.236%	$21.534	$21.53	$21.55	$21.50
Purchase #5	$110.90	13.705%	$126.0988	$126.10	$126.10	$126.10
Purchase #6	$134.35	13.239%	$152.1366	$152.14	$152.15	$152.10
Purchase #7	$137.39	13.492%	$155.9267	$155.93	$155.95	$155.90
7 purchase totals =	$906.60		$997.2925	$997.29	$997.35	$997.20