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	$20.46	5.408%	$21.5665	$21.57	$21.55	$21.60
Purchase #2	$19.36	9.837%	$21.2644	$21.26	$21.25	$21.30
Purchase #3	$87.43	9.622%	$95.8425	$95.84	$95.85	$95.80
Purchase #4	$185.71	8.172%	$200.8862	$200.89	$200.90	$200.90
Purchase #5	$42.91	5.405%	$45.2293	$45.23	$45.25	$45.20
Purchase #6	$245.67	9.686%	$269.4656	$269.47	$269.45	$269.50
Purchase #7	$207.78	13.711%	$236.2687	$236.27	$236.25	$236.30
7 purchase totals =	$809.32		$890.5232	$890.53	$890.50	$890.60