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	$53.34	12.302%	$59.9019	$59.90	$59.90	$59.90
Purchase #2	$153.45	9.845%	$168.5572	$168.56	$168.55	$168.60
Purchase #3	$27.95	7.659%	$30.0907	$30.09	$30.10	$30.10
Purchase #4	$41.51	3.845%	$43.1061	$43.11	$43.10	$43.10
Purchase #5	$9.85	7.330%	$10.572	$10.57	$10.55	$10.60
Purchase #6	$94.50	4.466%	$98.7204	$98.72	$98.70	$98.70
Purchase #7	$212.33	11.559%	$236.8732	$236.87	$236.85	$236.90
7 purchase totals =	$592.93		$647.8215	$647.82	$647.75	$647.90