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	$242.39	5.599%	$255.9614	$255.96	$255.95	$256.00
Purchase #2	$208.97	6.641%	$222.8477	$222.85	$222.85	$222.80
Purchase #3	$62.99	3.650%	$65.2891	$65.29	$65.30	$65.30
Purchase #4	$242.48	3.734%	$251.5342	$251.53	$251.55	$251.50
Purchase #5	$157.79	6.355%	$167.8176	$167.82	$167.80	$167.80
Purchase #6	$236.35	12.409%	$265.6787	$265.68	$265.70	$265.70
Purchase #7	$82.85	8.443%	$89.845	$89.85	$89.85	$89.80
7 purchase totals =	$1,233.82		$1,318.9737	$1,318.98	$1,319.00	$1,318.90