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	$136.98	6.216%	$145.4947	$145.49	$145.50	$145.50
Purchase #2	$248.70	6.212%	$264.1492	$264.15	$264.15	$264.10
Purchase #3	$97.51	6.237%	$103.5917	$103.59	$103.60	$103.60
Purchase #4	$99.27	13.306%	$112.4789	$112.48	$112.50	$112.50
Purchase #5	$248.31	4.125%	$258.5528	$258.55	$258.55	$258.60
Purchase #6	$181.36	3.746%	$188.1537	$188.15	$188.15	$188.20
Purchase #7	$211.98	10.136%	$233.4663	$233.47	$233.45	$233.50
7 purchase totals =	$1,224.11		$1,305.8873	$1,305.88	$1,305.90	$1,306.00