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	$117.82	5.650%	$124.4768	$124.48	$124.50	$124.50
Purchase #2	$168.75	9.564%	$184.8893	$184.89	$184.90	$184.90
Purchase #3	$66.26	7.816%	$71.4389	$71.44	$71.45	$71.40
Purchase #4	$49.32	10.803%	$54.648	$54.65	$54.65	$54.60
Purchase #5	$57.88	13.502%	$65.695	$65.70	$65.70	$65.70
Purchase #6	$9.76	4.222%	$10.1721	$10.17	$10.15	$10.20
Purchase #7	$121.57	8.483%	$131.8828	$131.88	$131.90	$131.90
7 purchase totals =	$591.36		$643.2029	$643.21	$643.25	$643.20