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	$210.31	5.649%	$222.1904	$222.19	$222.20	$222.20
Purchase #2	$82.90	8.577%	$90.0103	$90.01	$90.00	$90.00
Purchase #3	$74.46	7.675%	$80.1748	$80.17	$80.15	$80.20
Purchase #4	$45.44	13.420%	$51.538	$51.54	$51.55	$51.50
Purchase #5	$67.76	11.459%	$75.5246	$75.52	$75.50	$75.50
Purchase #6	$48.85	13.711%	$55.5478	$55.55	$55.55	$55.50
Purchase #7	$11.32	4.853%	$11.8694	$11.87	$11.85	$11.90
7 purchase totals =	$541.04		$586.8553	$586.85	$586.80	$586.80