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	$123.96	12.349%	$139.2678	$139.27	$139.25	$139.30
Purchase #2	$171.69	10.314%	$189.3981	$189.40	$189.40	$189.40
Purchase #3	$222.61	8.298%	$241.0822	$241.08	$241.10	$241.10
Purchase #4	$222.53	4.850%	$233.3227	$233.32	$233.30	$233.30
Purchase #5	$109.67	6.777%	$117.1023	$117.10	$117.10	$117.10
Purchase #6	$206.59	9.812%	$226.8606	$226.86	$226.85	$226.90
Purchase #7	$124.81	7.764%	$134.5002	$134.50	$134.50	$134.50
7 purchase totals =	$1,181.86		$1,281.5339	$1,281.53	$1,281.50	$1,281.60