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	$203.78	3.352%	$210.6107	$210.61	$210.60	$210.60
Purchase #2	$144.69	10.830%	$160.3599	$160.36	$160.35	$160.40
Purchase #3	$237.47	10.417%	$262.2072	$262.21	$262.20	$262.20
Purchase #4	$129.46	13.247%	$146.6096	$146.61	$146.60	$146.60
Purchase #5	$123.59	6.291%	$131.365	$131.37	$131.35	$131.40
Purchase #6	$10.88	7.848%	$11.7339	$11.73	$11.75	$11.70
Purchase #7	$48.82	10.609%	$53.9993	$54.00	$54.00	$54.00
7 purchase totals =	$898.69		$976.8856	$976.89	$976.85	$976.90