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	$36.69	11.289%	$40.8319	$40.83	$40.85	$40.80
Purchase #2	$173.71	6.584%	$185.1471	$185.15	$185.15	$185.10
Purchase #3	$250.56	5.690%	$264.8169	$264.82	$264.80	$264.80
Purchase #4	$94.60	3.816%	$98.2099	$98.21	$98.20	$98.20
Purchase #5	$136.50	5.411%	$143.886	$143.89	$143.90	$143.90
Purchase #6	$191.45	13.383%	$217.0718	$217.07	$217.05	$217.10
Purchase #7	$227.31	10.102%	$250.2729	$250.27	$250.25	$250.30
7 purchase totals =	$1,110.82		$1,200.2365	$1,200.24	$1,200.20	$1,200.20