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	$227.89	12.298%	$255.9159	$255.92	$255.90	$255.90
Purchase #2	$64.61	7.834%	$69.6715	$69.67	$69.65	$69.70
Purchase #3	$119.33	4.339%	$124.5077	$124.51	$124.50	$124.50
Purchase #4	$59.62	4.727%	$62.4382	$62.44	$62.45	$62.40
Purchase #5	$53.59	4.812%	$56.1688	$56.17	$56.15	$56.20
Purchase #6	$47.87	5.526%	$50.5153	$50.52	$50.50	$50.50
Purchase #7	$121.86	8.267%	$131.9342	$131.93	$131.95	$131.90
7 purchase totals =	$694.77		$751.1516	$751.16	$751.10	$751.10