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	$83.30	10.677%	$92.1939	$92.19	$92.20	$92.20
Purchase #2	$29.59	10.592%	$32.7242	$32.72	$32.70	$32.70
Purchase #3	$150.98	6.262%	$160.4344	$160.43	$160.45	$160.40
Purchase #4	$140.36	5.773%	$148.463	$148.46	$148.45	$148.50
Purchase #5	$144.80	11.136%	$160.9249	$160.92	$160.90	$160.90
Purchase #6	$245.32	5.231%	$258.1527	$258.15	$258.15	$258.20
Purchase #7	$240.39	4.337%	$250.8157	$250.82	$250.80	$250.80
7 purchase totals =	$1,034.74		$1,103.7088	$1,103.69	$1,103.65	$1,103.70