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	$19.60	4.421%	$20.4665	$20.47	$20.45	$20.50
Purchase #2	$41.86	7.820%	$45.1335	$45.13	$45.15	$45.10
Purchase #3	$191.82	11.488%	$213.8563	$213.86	$213.85	$213.90
Purchase #4	$220.86	9.720%	$242.3276	$242.33	$242.35	$242.30
Purchase #5	$100.76	8.786%	$109.6128	$109.61	$109.60	$109.60
Purchase #6	$51.91	3.828%	$53.8971	$53.90	$53.90	$53.90
Purchase #7	$249.60	13.370%	$282.9715	$282.97	$282.95	$283.00
7 purchase totals =	$876.41		$968.2653	$968.27	$968.25	$968.30