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	$112.85	10.149%	$124.3031	$124.30	$124.30	$124.30
Purchase #2	$35.37	12.722%	$39.8698	$39.87	$39.85	$39.90
Purchase #3	$31.61	9.159%	$34.5052	$34.51	$34.50	$34.50
Purchase #4	$160.27	4.524%	$167.5206	$167.52	$167.50	$167.50
Purchase #5	$45.81	6.624%	$48.8445	$48.84	$48.85	$48.80
Purchase #6	$73.98	7.196%	$79.3036	$79.30	$79.30	$79.30
Purchase #7	$56.37	10.452%	$62.2618	$62.26	$62.25	$62.30
7 purchase totals =	$516.26		$556.6086	$556.60	$556.55	$556.60