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	$128.53	4.772%	$134.6635	$134.66	$134.65	$134.70
Purchase #2	$65.39	6.353%	$69.5442	$69.54	$69.55	$69.50
Purchase #3	$217.36	7.148%	$232.8969	$232.90	$232.90	$232.90
Purchase #4	$6.61	7.839%	$7.1282	$7.13	$7.15	$7.10
Purchase #5	$153.97	12.629%	$173.4149	$173.41	$173.40	$173.40
Purchase #6	$100.73	10.714%	$111.5222	$111.52	$111.50	$111.50
Purchase #7	$91.80	9.629%	$100.6394	$100.64	$100.65	$100.60
7 purchase totals =	$764.39		$829.8093	$829.80	$829.80	$829.70