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	$55.33	8.284%	$59.9135	$59.91	$59.90	$59.90
Purchase #2	$178.98	9.406%	$195.8149	$195.81	$195.80	$195.80
Purchase #3	$229.41	13.572%	$260.5455	$260.55	$260.55	$260.50
Purchase #4	$68.64	4.285%	$71.5812	$71.58	$71.60	$71.60
Purchase #5	$168.86	10.250%	$186.1682	$186.17	$186.15	$186.20
Purchase #6	$93.98	5.807%	$99.4374	$99.44	$99.45	$99.40
Purchase #7	$85.87	3.488%	$88.8651	$88.87	$88.85	$88.90
7 purchase totals =	$881.07		$962.3258	$962.33	$962.30	$962.30