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	$230.92	8.681%	$250.9662	$250.97	$250.95	$251.00
Purchase #2	$98.74	4.174%	$102.8614	$102.86	$102.85	$102.90
Purchase #3	$35.93	7.164%	$38.504	$38.50	$38.50	$38.50
Purchase #4	$211.42	12.320%	$237.4669	$237.47	$237.45	$237.50
Purchase #5	$36.82	13.693%	$41.8618	$41.86	$41.85	$41.90
Purchase #6	$224.43	3.510%	$232.3075	$232.31	$232.30	$232.30
Purchase #7	$105.77	6.345%	$112.4811	$112.48	$112.50	$112.50
7 purchase totals =	$944.03		$1,016.4489	$1,016.45	$1,016.40	$1,016.60