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	$25.98	5.840%	$27.4972	$27.50	$27.50	$27.50
Purchase #2	$85.94	4.142%	$89.4996	$89.50	$89.50	$89.50
Purchase #3	$127.79	4.684%	$133.7757	$133.78	$133.80	$133.80
Purchase #4	$228.68	13.186%	$258.8337	$258.83	$258.85	$258.80
Purchase #5	$160.68	3.237%	$165.8812	$165.88	$165.90	$165.90
Purchase #6	$70.44	13.197%	$79.736	$79.74	$79.75	$79.70
Purchase #7	$92.64	6.700%	$98.8469	$98.85	$98.85	$98.80
7 purchase totals =	$792.15		$854.0703	$854.08	$854.15	$854.00