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	$230.93	11.107%	$256.5794	$256.58	$256.60	$256.60
Purchase #2	$156.46	4.817%	$163.9967	$164.00	$164.00	$164.00
Purchase #3	$245.69	13.256%	$278.2587	$278.26	$278.25	$278.30
Purchase #4	$243.90	10.454%	$269.3973	$269.40	$269.40	$269.40
Purchase #5	$248.98	9.779%	$273.3278	$273.33	$273.35	$273.30
Purchase #6	$210.40	8.417%	$228.1094	$228.11	$228.10	$228.10
Purchase #7	$56.39	5.418%	$59.4452	$59.45	$59.45	$59.40
7 purchase totals =	$1,392.75		$1,529.1145	$1,529.13	$1,529.15	$1,529.10