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	$87.88	13.580%	$99.8141	$99.81	$99.80	$99.80
Purchase #2	$233.53	9.356%	$255.3791	$255.38	$255.40	$255.40
Purchase #3	$188.94	5.290%	$198.9349	$198.93	$198.95	$198.90
Purchase #4	$73.39	6.531%	$78.1831	$78.18	$78.20	$78.20
Purchase #5	$211.88	10.260%	$233.6189	$233.62	$233.60	$233.60
Purchase #6	$92.92	7.856%	$100.2198	$100.22	$100.20	$100.20
Purchase #7	$135.54	5.828%	$143.4393	$143.44	$143.45	$143.40
7 purchase totals =	$1,024.08		$1,109.5892	$1,109.58	$1,109.60	$1,109.50