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	$97.28	5.388%	$102.5214	$102.52	$102.50	$102.50
Purchase #2	$203.70	3.718%	$211.2736	$211.27	$211.25	$211.30
Purchase #3	$163.64	9.696%	$179.5065	$179.51	$179.50	$179.50
Purchase #4	$57.92	12.476%	$65.1461	$65.15	$65.15	$65.10
Purchase #5	$118.78	4.486%	$124.1085	$124.11	$124.10	$124.10
Purchase #6	$175.35	6.538%	$186.8144	$186.81	$186.80	$186.80
Purchase #7	$247.69	13.314%	$280.6674	$280.67	$280.65	$280.70
7 purchase totals =	$1,064.36		$1,150.0379	$1,150.04	$1,149.95	$1,150.00