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	$42.26	3.718%	$43.8312	$43.83	$43.85	$43.80
Purchase #2	$125.64	3.504%	$130.0424	$130.04	$130.05	$130.00
Purchase #3	$83.72	8.369%	$90.7265	$90.73	$90.75	$90.70
Purchase #4	$67.32	11.383%	$74.983	$74.98	$75.00	$75.00
Purchase #5	$57.97	8.282%	$62.7711	$62.77	$62.75	$62.80
Purchase #6	$75.97	8.177%	$82.1821	$82.18	$82.20	$82.20
Purchase #7	$48.93	13.360%	$55.467	$55.47	$55.45	$55.50
7 purchase totals =	$501.81		$540.0033	$540.00	$540.05	$540.00