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	$36.40	7.768%	$39.2276	$39.23	$39.25	$39.20
Purchase #2	$99.28	12.598%	$111.7873	$111.79	$111.80	$111.80
Purchase #3	$161.71	13.673%	$183.8206	$183.82	$183.80	$183.80
Purchase #4	$22.28	13.192%	$25.2192	$25.22	$25.20	$25.20
Purchase #5	$200.69	7.329%	$215.3986	$215.40	$215.40	$215.40
Purchase #6	$39.86	10.753%	$44.1461	$44.15	$44.15	$44.10
Purchase #7	$154.79	9.737%	$169.8619	$169.86	$169.85	$169.90
7 purchase totals =	$715.01		$789.4613	$789.47	$789.45	$789.40