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	$220.45	11.284%	$245.3256	$245.33	$245.35	$245.30
Purchase #2	$139.60	5.714%	$147.5767	$147.58	$147.60	$147.60
Purchase #3	$245.80	9.225%	$268.4751	$268.48	$268.50	$268.50
Purchase #4	$40.31	6.149%	$42.7887	$42.79	$42.80	$42.80
Purchase #5	$86.77	11.718%	$96.9377	$96.94	$96.95	$96.90
Purchase #6	$12.97	3.636%	$13.4416	$13.44	$13.45	$13.40
Purchase #7	$63.33	3.566%	$65.5883	$65.59	$65.60	$65.60
7 purchase totals =	$809.23		$880.1337	$880.15	$880.25	$880.10