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	$243.74	4.630%	$255.0252	$255.03	$255.05	$255.00
Purchase #2	$167.40	12.834%	$188.8841	$188.88	$188.90	$188.90
Purchase #3	$6.53	11.491%	$7.2804	$7.28	$7.30	$7.30
Purchase #4	$217.67	13.427%	$246.8966	$246.90	$246.90	$246.90
Purchase #5	$91.98	9.267%	$100.5038	$100.50	$100.50	$100.50
Purchase #6	$57.94	3.346%	$59.8787	$59.88	$59.90	$59.90
Purchase #7	$120.46	5.822%	$127.4732	$127.47	$127.45	$127.50
7 purchase totals =	$905.72		$985.9420	$985.94	$986.00	$986.00