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	$99.73	11.706%	$111.4044	$111.40	$111.40	$111.40
Purchase #2	$103.41	10.543%	$114.3125	$114.31	$114.30	$114.30
Purchase #3	$170.49	13.153%	$192.9145	$192.91	$192.90	$192.90
Purchase #4	$123.49	4.111%	$128.5667	$128.57	$128.55	$128.60
Purchase #5	$41.85	5.620%	$44.202	$44.20	$44.20	$44.20
Purchase #6	$248.69	8.752%	$270.4553	$270.46	$270.45	$270.50
Purchase #7	$14.90	6.813%	$15.9151	$15.92	$15.90	$15.90
7 purchase totals =	$802.56		$877.7705	$877.77	$877.70	$877.80