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	$57.43	3.616%	$59.5067	$59.51	$59.50	$59.50
Purchase #2	$128.88	5.629%	$136.1347	$136.13	$136.15	$136.10
Purchase #3	$22.89	8.716%	$24.8851	$24.89	$24.90	$24.90
Purchase #4	$93.72	7.458%	$100.7096	$100.71	$100.70	$100.70
Purchase #5	$77.84	7.792%	$83.9053	$83.91	$83.90	$83.90
Purchase #6	$182.41	13.496%	$207.0281	$207.03	$207.05	$207.00
Purchase #7	$142.53	3.433%	$147.4231	$147.42	$147.40	$147.40
7 purchase totals =	$705.70		$759.5926	$759.60	$759.60	$759.50