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	$153.68	4.574%	$160.7093	$160.71	$160.70	$160.70
Purchase #2	$220.86	13.526%	$250.7335	$250.73	$250.75	$250.70
Purchase #3	$47.92	9.599%	$52.5198	$52.52	$52.50	$52.50
Purchase #4	$94.86	6.210%	$100.7508	$100.75	$100.75	$100.80
Purchase #5	$7.25	8.724%	$7.8825	$7.88	$7.90	$7.90
Purchase #6	$58.85	4.416%	$61.4488	$61.45	$61.45	$61.40
Purchase #7	$25.53	12.363%	$28.6863	$28.69	$28.70	$28.70
7 purchase totals =	$608.95		$662.7310	$662.73	$662.75	$662.70